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Title: Ultrafast Dynamics in Warm Dense Matter Materials and Halide Perovskite.
Creator: Li, Dong, Cao, Jianming, Yang, Wei, Bonesteel, N. E., Chiorescu, Irinel, Florida State University, College of Arts and Sciences, Department of Physics
Abstract/Description: The dissertation presents the recent development of the third-generation femtosecond electron diffractometer in Professor Jim Cao's group. Two techniques, femtosecond electron shadow imaging and deflectometry (FESID) and femtosecond electron diffraction (FED), were developed and applied to study ultrafast dynamics in laser-induced warm dense matter and quantum dots in real time. FESID provides both a global view and local prospect of the transient electric field, associated with laser-induced...
Show moreThe dissertation presents the recent development of the third-generation femtosecond electron diffractometer in Professor Jim Cao's group. Two techniques, femtosecond electron shadow imaging and deflectometry (FESID) and femtosecond electron diffraction (FED), were developed and applied to study ultrafast dynamics in laser-induced warm dense matter and quantum dots in real time. FESID provides both a global view and local prospect of the transient electric field, associated with laser-induced electron emission. The research activities cover two main objects: dynamics of ejected electron expansion from warm dense nanofilms and hyperthermal electron transport mechanisms in warm dense nanofilms. With FED, we measure laser-induced ultrafast structural dynamics of halide perovskite CsPbBr3 in real time. In the first project, we conduct ultrafast electron shadow imaging and deflection measurements of the laser-produced warm dense copper nanofilm. The results show that a significant number of electrons is ejected from the nanofilm, forming electron clouds of hundreds of microns on both sides of the pumped film. Furthermore, even for a thin 30-nm copper film, we find that the electron clouds develop asymmetry between the pumped front side and the rear side at the pump fluence of 4.5 J/cm2. The possible mechanisms leading to this ejected charge asymmetry and its implication are discussed. Next, we report a systematic study of the ejected charge dynamics surrounding laser produced 30-nm warm dense gold films using single-shot femtosecond electron shadow imaging and deflectometry. The results reveal a two-step dynamical process of the ejected electrons under the high pump fluence conditions: an initial emission and accumulation of a large number of electrons near the pumped surface region followed by the formation of hemispherical clouds of electrons on both sides of the film, which escape into the vacuum at a nearly isotropic and constant velocity with an unusually high kinetic energy of more than 300 eV. We also develop a model of the escaping charge distribution that not only reproduces the main features of the observed charge expansion dynamics but also allows us to extract the number of ejected electrons remaining in the cloud. In the second project, we investigate hyperthermal electron transport by single-shot measurements of warm dense gold and aluminum nanofilms using ultrafast electron shadow imaging and deflectometry. The results show a clear fluence limit of 0.26 J/cm2 and 0.83 J/cm2 for ballistic transport of nonthermal electrons for both two metals, respectively. This nonuniform heating is attributed to diffusive electrons. The last project, we have measured the ultrafast structural dynamics in halide perovskite CsPbBr3 in real time with Femtosecond electron diffraction. We observed CsPbBr3 experience significant ultrafast impulsive heating. This heating causes the CsPbBr3 to undergo an orthorhombic-to-cubic phase transition observable through FED. The photo induced phase transition occurs on the timescale of 1.1 ± 0.3 ps at fluences of 2.5 mJ/cm2.
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Date Issued: 2019
Identifier: 2019_Summer_Li_fsu_0071E_15420
Format: Thesis

Title: Magnetic Ordering and Magnetotransport at Molecular and Nano Scales.
Creator: Simmons, Danielle Theresa, Xiong, Peng, Shatruk, Mykhailo, Bonesteel, N. E., Baumbach, Ryan E., Piekarewicz, Jorge, Florida State University, College of Arts and Sciences,...
Show moreSimmons, Danielle Theresa, Xiong, Peng, Shatruk, Mykhailo, Bonesteel, N. E., Baumbach, Ryan E., Piekarewicz, Jorge, Florida State University, College of Arts and Sciences, Department of Physics
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Abstract/Description: The understanding of magnetic materials has become crucial to both fundamental physics and technological advancement. Particularly, the interplay between magnetic and electronic properties has given rise to such novel physics as high temperature superconductivity and colossal magnetoresistance. Some magnetic materials potentially hold the key to the realization of new nanoscale memory and logic devices. Specifically, spintronics and molecular electronics are two fields drawing increasing...
Show moreThe understanding of magnetic materials has become crucial to both fundamental physics and technological advancement. Particularly, the interplay between magnetic and electronic properties has given rise to such novel physics as high temperature superconductivity and colossal magnetoresistance. Some magnetic materials potentially hold the key to the realization of new nanoscale memory and logic devices. Specifically, spintronics and molecular electronics are two fields drawing increasing attention due to their potential to address the ever-increasing need for continued device miniaturization. This dissertation focuses on probing magnetic ordering and magnetotransport at molecular and nano scales utilizing electronic measurement techniques in order to gain further understanding of these complex phenomena. The first project of this dissertation deals with the effect of electronic phase separation (EPS), which is believed to be at the root of several emergent correlated electron phenomena. The goal of this research is to gain further insight into the complex interplay between the magnetic and electronic interactions in the ferromagnetic semimetal EuB6 under applied hydrostatic pressure. Previous studies under ambient pressure have uncovered a remarkable manifestation of EPS in the nonlinear Hall effect of EuB6. The magnetotransport measurements under pressure that we performed revealed an increase in carrier concentration as well as an increase in the critical magnetization needed to instigate the percolation of the phase-separated ferromagnetic entities (magnetic polarons). Also discovered by these measurements was an intermediate state between the paramagnetic insulating phase and the ferromagnetic metallic phase, thereby indicating that the electronic phase separation is even more complicated than previously predicted. Previous work had shown a lattice constriction concomitant with the formation and percolation of magnetic polarons, suggesting that magnetostriction might provide a direct probe of their formation. These results inspired us to measure the magnetostriction of EuB6 under applied pressure in the phase-separated regions. Not only did our measurements show a reduction in the constriction necessary for polaron formation, but also showed lattice expansion above and below the polaron formation temperatures. While hybrid organic-electronic devices hold much promise in a variety of applications, there are several hurdles to overcome before they can be fully integrated. One such family of materials, known as spin-crossover molecules, have high-spin and low-spin states that can be activated thermally and/or through photo excitation. Since each molecule has an independent spin state, devices built from these materials would not rely on long-range magnetic order. Additionally, advancements in molecular nano-patterning and self-assembly make these molecules attractive for bottom-up device integration. On the other hand, the tiny magnetic signals from the change of spin state of a small volume of molecules necessitate more sensitive devices for measuring nano patterns of monolayers of the molecules. In the second project of the dissertation, we demonstrate the feasibility of magnetic measurements of monolayers of spin-crossover molecules. Using a high-sensitivity Hall magnetometry technique, we showed measurements of the light induced excited spin state trapping effect in Fe(ptz)6(BF4)2. These experiments provide clear guidelines for improving the magnetic moment sensitivity by using semiconductor heterostructures free of photoconductivity.
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Date Issued: 2019
Identifier: 2019_Spring_Simmons_fsu_0071E_13940
Format: Thesis

Title: Tuning Intertwined Energy Scales in f-Electron Systems by Chemical Substitution.
Creator: Lai, You, Baumbach, Ryan E., Xiong, Peng, Shatruk, Mykhailo, Graf, David, Schlottmann, Pedro U., Riley, Mark A., Florida State University, College of Arts and Sciences,...
Show moreLai, You, Baumbach, Ryan E., Xiong, Peng, Shatruk, Mykhailo, Graf, David, Schlottmann, Pedro U., Riley, Mark A., Florida State University, College of Arts and Sciences, Department of Physics
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Abstract/Description: Materials that contain f-electron elements often exhibit complex phase diagrams with different phenomena including nematic electronic states, charge and spin instabilities, the breakdown of Fermi liquid behavior, and unconventional superconductivity. This diversity of behavior is related to the fine balance between several factors including the magnetic exchange, Kondo effect, crystal electric field splitting and strong spin-orbit coupling. As a result, many such systems exhibit intertwined...
Show moreMaterials that contain f-electron elements often exhibit complex phase diagrams with different phenomena including nematic electronic states, charge and spin instabilities, the breakdown of Fermi liquid behavior, and unconventional superconductivity. This diversity of behavior is related to the fine balance between several factors including the magnetic exchange, Kondo effect, crystal electric field splitting and strong spin-orbit coupling. As a result, many such systems exhibit intertwined order parameters that are controllable through pressure, magnetic field, and chemical substitution. Here, we report results from chemical substitution studies in three distinct Kondo lattice systems. In each case, we are able to suppress an ordered state towards zero temperature at a possible quantum phase transition and study the resulting behavior. For CeCu$_2$Si$_2$, Si $\rightarrow$ P chemical substitution compresses the unit cell volume while adding $s/p$ electrons. This encourages complex magnetism and drives the system away from a quantum critical point. These results are understood by considering that the electronic hybridization between the f- and conduction electrons in this system is controlled by nearly independent parameters of unit cell volume and s; p; d shell filling, which drive the system's behavior along different axes. For CePd$_2$P$_2$, Pd $\rightarrow$ Ni substitution suppresses the ferromagnetism towards a disordered ferromagnetic QCP at $x_{\rm{cr}}$ = 0.7, where the breakdown of Fermi liquid behavior is observed. We also find that for CePd$_2$P$_2$, a pressure of $P_{\rm{c}}$ = 12 GPa would likely be sufficient to access a quantum phase transition. These results provide a useful experimental testbed for the Belitz-Kirkpatrick-Vojta (BKV) theory. For UCr$_2$Si$_2$, Cr $\rightarrow$ Ru substitution results in filling of the $d$-shell without significantly changing the unit cell volume. This suppresses the antiferromagnetic order $T_{\rm{N}}$ ($T_{\rm{N}}$ $\approx$ 24 K for UCr$_2$Si$_2$) and the structural phase transition $T_{\rm{S}}$ ($T_{\rm{S}}$ $\approx$ 200 K for UCr$_2$Si$_2$) that are seen in the parent compound. $T_{\rm{N}}$ approaches zero temperature near $x_{\rm{c, N}}$ = 0.08 while $T_{\rm{S}}$ reaches a minimum value near $x_{\rm{c, S}}$ = 0.16, after which the structural phase transition disappears for larger $x$. Near this concentration there is evidence for the breakdown of Fermi liquid behavior in the transport and heat capacity measurements, suggesting that this may be a model system for studying a lattice instability at zero temperature, its relationship to a nearby antiferromagnetic quantum critical point, and the resulting impact on electronic properties and lattice modes in a strongly correlated electron metal.
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Date Issued: 2019
Identifier: 2019_Spring_Lai_fsu_0071E_15055
Format: Thesis

Title: Topological Quantum Phase Transitions and Quench Dynamics.
Creator: Liou, Shiuan-Fan, Yang, Kun, Siegrist, Theo, Bonesteel, N. E., Balicas, Luis, Engel, Lloyd W., Xiong, Peng, Florida State University, College of Arts and Sciences, Department of...
Show moreLiou, Shiuan-Fan, Yang, Kun, Siegrist, Theo, Bonesteel, N. E., Balicas, Luis, Engel, Lloyd W., Xiong, Peng, Florida State University, College of Arts and Sciences, Department of Physics
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Abstract/Description: Topological phases of matter and the phase transitions between them have been the focus of much recent theoretical and experimental interest. In this thesis, we firstly study a type of topological phase transitions between quantum Hall states driven by pairing interactions through Feshbach resonances. Although quantum Hall effects were first discovered in electronic condensed matter systems, this type of phase transitions was proposed to ultra cold atom field for their ability of the control...
Show moreTopological phases of matter and the phase transitions between them have been the focus of much recent theoretical and experimental interest. In this thesis, we firstly study a type of topological phase transitions between quantum Hall states driven by pairing interactions through Feshbach resonances. Although quantum Hall effects were first discovered in electronic condensed matter systems, this type of phase transitions was proposed to ultra cold atom field for their ability of the control of interactions. In addition, we also investigate the quench dynamics of topological phase transitions based on specifically Haldane model and checkerboard model in the second part. In the study of topological phase transitions between fermionic integer quantum Hall (FIQH) and bosonic fractional quantum Hall (BFQH) phases, we first provide a general picture of this kind of quantum Hall phase transitions. Subsequently, we use exact diagonalization to study the quantum phases and phase transitions when a single species of fermionic atoms at Landau level filling factor vf = 1 in a rotating trap interact through a p-wave Feshbach resonance. We show that under weak pairing interaction, the system undergoes a second order quantum phase transition from vf = 1 fermionic integer quantum Hall (FIQH) state at positive detuning, to vb = ¼ bosonic fractional quantum Hall (BFQH) state at negative detuning. However, when the pairing interaction increases, a new phase between them emerges, corresponding to a fraction of fermionic atoms stay in a coherent superposition of bosonic molecule state and an unbound pair. The phase transition from FIQH phase to the new phase is of second order and that from the new phase to BFQH phase is of first order. Furthermore, we investigate the quantum phases and phase transition in a system made of two species of fermionic atoms that interact with each other via s-wave Feshbach resonance, and are subject to rotation or a synthetic gauge field that puts the fermions at Landau level filling factor vf = 2. We show that the system undergoes a continuous quantum phase transition from a vf = 2 fermionic integer quantum Hall state formed by atoms, to a vf = ½ bosonic fractional quantum Hall state formed by bosonic diatomic molecules. In the disk geometry we use, these two different topological phases are distinguished by their different gapless edge excitation spectra, and the quantum phase transition between them is signaled by the closing of the energy gap in the bulk. Comparisons will be made with field theoretical predictions, and the case of p-wave pairing. In the second part of this thesis, we study the dynamics of systems quenched through topological quantum phase transitions and investigate the behavior of the bulk and edge excitations with various quench rates. Specifically, we consider the Haldane model and checkerboard model in slow quench processes with distinct band-touching structures leading to topology changes. The generation of bulk excitations is found to obey the power-law relation Kibble-Zurek and Landau-Zener theories predict. However, an anti-Kibble-Zurek behavior is observed in the edge excitations. The mechanism of excitation generation on edge states is revealed, which explains the anti-Kibble-Zurek behavior.
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Date Issued: 2019
Identifier: 2019_Spring_Liou_fsu_0071E_15071
Format: Thesis

Title: Backbending, Seniority and Pauli Blocking of Pairing Correlations at High Rotational Frequencies in Rapidly Rotating Nuclei: A Systematic Analysis of Er, Yb, Hf and W Isotopes and Nuclear Structure Studies of ¹⁷⁹, ¹⁸⁰W, ¹⁶⁰, ¹⁶¹Gd and ¹⁵⁵Sm.
Creator: Villafana, Kalisa A. (Kalisa Aneika), Riley, Mark A., Plewa, Tomasz, Bonesteel, N. E., Piekarewicz, Jorge, Florida State University, College of Arts and Sciences, Department of...
Show moreVillafana, Kalisa A. (Kalisa Aneika), Riley, Mark A., Plewa, Tomasz, Bonesteel, N. E., Piekarewicz, Jorge, Florida State University, College of Arts and Sciences, Department of Physics
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Abstract/Description: The goal of nuclear structure experiments is to understand how properties of nuclei evolve as a function of key observables such as proton and neutron numbers, deformation, angular momentum and excitation energy, to name a few. In order to investigate how the nuclear structure evolves with these parameters, γ-ray spectroscopy can be utilized, which requires efficient γ-ray detection systems. This thesis details γ-ray spectroscopy to investigate the nuclear structure in a series of rare-earth...
Show moreThe goal of nuclear structure experiments is to understand how properties of nuclei evolve as a function of key observables such as proton and neutron numbers, deformation, angular momentum and excitation energy, to name a few. In order to investigate how the nuclear structure evolves with these parameters, γ-ray spectroscopy can be utilized, which requires efficient γ-ray detection systems. This thesis details γ-ray spectroscopy to investigate the nuclear structure in a series of rare-earth nuclei using state of the art γ-ray detector systems. In the first part of this thesis, high-spin states in ¹⁷⁹, ¹⁸⁰W (Z=74) produced via fusion-evaporation reactions carried out at Florida State University's John D. Fox Laboratory are discussed. The reaction used to produce excited states in these nuclei was a 14C beam on an enriched ¹⁷⁰Er target, and the 5n and 4n evaporation channels were studied to investigate ¹⁷⁹, ¹⁸⁰W respectively. The emitted γ-rays were detected using three Compton-suppressed clover detectors and seven single element Compton-suppressed high-purity germanium detectors. In this experiment, 852 million γ-γ coincidences and 82 million γ-γ-γ coincidences at 75 MeV beam energy were collected. Additionally, at a beam energy of 68 MeV, 119 million γ-γ coincidences and 9.6million γ-γ-γ coincidences. The primary purpose of this experiment was to add to a systematic investigation of band crossing frequencies in heavy tungsten nuclei in order to observe the effect of quasiparticle seniority and high rotational frequencies on pairing correlations. Additionally, due in part to results obtained from the first part of this analysis, new systematic data in the A ≈ 160 − 180 region is also discussed, with an emphasis on the role that pair-blocking effects play during the rotation of the nucleus. This systematic investigation builds upon the classic findings of Garrett et al. [1] who investigated systematically the critical band crossing frequencies resulting from the rotational alignment of the first pair of i₁₃/₂ neutrons (AB) in rare-earth nuclei. In that study, evidence was found for an odd-even neutron number dependence attributed to changes in the strength of neutron pairing correlations. The present work carries out a similar investigation at higher rotational frequencies for the second pair of aligning i₁₃/₂ neutrons (BC), advancing the work started by Scott Miller, formerly of the Riley group [2]. Again, a systematic difference in band crossing frequencies is observed between odd-N and even-N Er, Yb, Hf, and W nuclei, but in the BC case, it is opposite to the AB neutron-number dependence. These results are discussed in terms of a reduction of neutron pairing correlations at high rotational frequencies and of the effects of Pauli blocking on the pairing field by higher-seniority configurations. Also playing a significant role are the changes in deformation with proton and neutron number, the changes of location of single-particle orbitals as a function of quadrupole deformation, and the position of the Fermi surface with regard to the various Ω (projection of total angular momentum I onto the symmetry axis) components of the neutron i₁₃/₂ shell. The second part of this thesis discusses in detail the nuclear structure of ¹⁶⁰Gd and highlights some new band structures in ¹⁵⁵Sm and ¹⁶¹Gd. Two reactions were carried out to produce a multitude of neutron-rich isotopes performed at the Argonne Tandem Linear Accelerator System (ATLAS) at Argonne National Laboratory (ANL). Firstly, a ¹⁶⁰Gd beam of energy at 1000 MeV was impinged on a ¹⁵⁴Sm target and then in a second experiment on a ¹⁶⁴Dy target. The goal of the deep-inelastic collisions was to provide a mechanism to reach a number of neutron-rich isotopes, in particular those from the mid-shell region in rare-earth nuclei. Although many neutron-rich nuclei were produced, they were not populated strongly enough to see new results. However, a byproduct of the reactions was the strong Coulomb excitation of the 160 Gd beam. Many excited states in ¹⁶⁰Gd were produced, and as a result, a spectroscopic analysis of 160Gd was carried out, and will be discussed in detail in this thesis. Additionally, new γ-ray transitions in other isotopes such as ¹⁵⁵Sm and ¹⁶¹Gd were also produced and will be discussed. The Gammasphere detector array was used to detect γ-rays from the excited nuclei, because of its sensitivity to cleanly delineate the vast number of multi-nucleon transfer reaction channels. As a result of both analysis, many new decay transitions and new energy levels were observed in the aforementioned nuclei. Whenever possible, the intensities, angular correlations, spins, parities, and rotational behaviors of these newly discovered states were analyzed.
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Date Issued: 2019
Identifier: 2019_Summer_Villafana_fsu_0071E_15455
Format: Thesis

Title: Beyond the Standard Model of Particles: Effective Field Theories and Baryogenesis.
Creator: Yunesi, Arash, Agashe, Amod S. (Amod Sadanand), Reina, Laura, Huffenberger, Kevin M., Florida State University, College of Arts and Sciences, Department of Physics
Abstract/Description: Two big questions in physics beyond the Standard Model of particles are nature of Dark Matter and a theory of Quantum Gravity. In this work, topics related to both of these improtant questions are presented. First, we introduce an effective theory for soft and collinear limits of gravitational scatterings. It is a well-known fact that amplitudes including gravitons are inherently difficult to calculate. Our effective theory in its target phase space, substantially simplifies calculations of...
Show moreTwo big questions in physics beyond the Standard Model of particles are nature of Dark Matter and a theory of Quantum Gravity. In this work, topics related to both of these improtant questions are presented. First, we introduce an effective theory for soft and collinear limits of gravitational scatterings. It is a well-known fact that amplitudes including gravitons are inherently difficult to calculate. Our effective theory in its target phase space, substantially simplifies calculations of scattering amplitudes including gravtions. Our step by step procedure gives all the relevant operators at leading and next to leading powers for any full theory that couples to gravitons. In addition, the soft graviton theorem and decoupling of collinear gravitons at the leading power are manifest from the outset in the effective symmetries of the theory. At the next-to-leading power, certain simple structures of amplitudes, which are completely obscure in Feynman diagrams of the full theory, are also revealed. We will also discuss how ambiguity in choice of light-cone coordinates introduces fundamental redundancies in Soft Collinear Effective Theory (SCET). SCET Lagrangian should be invariant under these transformations of coordinates, and the constraints from these transformations further reduce calculations needed for a scattering process. Second, thermal freeze-out of WIMPs can provide a unified origin of dark matter and baryon abundances in our universe. We show that this mechanism exhibits rich collider phenomenology. The collider signatures we point out can be tested at the current and future experiments at the LHC, even if the WIMPs are not charged under Standard Model and higgs interactions. In particular, the simplest such implementation can already offer a very clean signal of a TeV-scale resonance that decays to diphotons with a cross section that can easily be within the reach of the current and near-future LHC runs in the region of parameter space that leads to a successful baryogenesis. Other characteristic signatures include the production of multi-bottom and/or multi-top quarks, promptly or displaced. An even more exotic possibility is the production of two separate sets of isolated emerging jets connected by a charged track, which may require new dedicated studies. Finally, di-nucleon decay can also provide a powerful probe of the mechanism.
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Date Issued: 2019
Identifier: 2019_Summer_Yunesi_fsu_0071E_15396
Format: Thesis

Title: Quench Protection of Bi2Sr2CaCu2O8+X High Temperature Superconducting Magnets.
Creator: Davis, Daniel S. (Daniel Scott), Larbalestier, D. (David), Chiorescu, Irinel, Trociewitz, Ulf P (Ulf Peter Trociewitz), Owens, Joseph F. (Joseph Francis), Riley, Mark A.,...
Show moreDavis, Daniel S. (Daniel Scott), Larbalestier, D. (David), Chiorescu, Irinel, Trociewitz, Ulf P (Ulf Peter Trociewitz), Owens, Joseph F. (Joseph Francis), Riley, Mark A., Latturner, Susan, Florida State University, College of Arts and Sciences, Department of Physics
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Abstract/Description: High temperature superconductors (HTS) allow for the construction of magnets generating fields of more than 30 T, enabling the investigation of new phenomena in condensed matter science and high energy physics. High field magnets store large amounts of energy that must be dissipated if the field collapses, but HTS materials require large quantities of heat for transitioning to the normal state. This makes HTS conductors very stable against fluctuations, yet difficult to protect from extreme...
Show moreHigh temperature superconductors (HTS) allow for the construction of magnets generating fields of more than 30 T, enabling the investigation of new phenomena in condensed matter science and high energy physics. High field magnets store large amounts of energy that must be dissipated if the field collapses, but HTS materials require large quantities of heat for transitioning to the normal state. This makes HTS conductors very stable against fluctuations, yet difficult to protect from extreme temperature rise in the case that something generates a propagating normal or resistive zone in the magnet, i.e. quenches the superconductor. As HTS conductor is much more expensive than normal conductors or low temperature superconductors (LTS), protecting even prototype research coils and especially large-scale user solenoids and accelerator dipoles is paramount. Recently, a quench protection system relying on interfilament coupling currents within superconductors has been developed with LTS magnet systems. Coupling-loss induced quench (CLIQ) protection attempts to safely distribute the stored energy of a superconducting magnet over a larger volume by quickly bringing a significant fraction into the normal state by introducing oscillating currents into sections of the magnet generating heat due to the rapidly varying magnetic field. As HTS have larger energy margins to the normal state, in addition to different AC loss characteristics and conductor geometries, experiments and simulations are underway to evaluate and optimize AC loss induced quench for each conductor. Addressing the pressing need for reliable high field HTS magnets, presented here are the results for implementing these systems in magnets made from Bi2Sr2CaCu2O8+x (Bi-2212), which is the practical HTS most similar to LTS in both single strand and cable designs. Recent advances in the current carrying capacity of Bi-2212 (>1000 A mm^-2 at 5 T) due to improved starting powder and over-pressure heat treatment make this HTS appealing for large-scale magnet projects. Long sample conductor property measurements are underway to investigate if Bi-2212 has consistent electrical and mechanical properties along its length. Collaboration between the National High Magnetic Field Laboratory (NHMFL) and Lawrence Berkeley National Laboratory (LBL) has allowed for testing on world-record sub-scale accelerator dipoles and test coils for a program working towards generating more than 1 GHz NMR spectra and fields in excess of 30 T.
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Date Issued: 2019
Identifier: 2019_Summer_Davis_fsu_0071E_15413
Format: Thesis

Title: Photoresponse and Charge Transport in Halide Perovskites.
Creator: Wang, Xi, Gao, Hanwei, Hellstrom, Eric, Bonesteel, N. E., Piekarewicz, Jorge, Xiong, Peng, Florida State University, College of Arts and Sciences, Department of Physics
Abstract/Description: Halide Perovskites have recently risen as a new class of optoelectronic materials. Remarkable optical and electrical properties have led to the demonstration of various perovskite-based devices such as solar cells1, LEDs2-5, photodetectors6 and lasers7,8. Particularly, perovskite solar cells have reached >24% of the energy conversion efficiency and outperformed most of the single-junction thin film solar cells available on the market1. Unfortunately, most of the perovskite-based devices...
Show moreHalide Perovskites have recently risen as a new class of optoelectronic materials. Remarkable optical and electrical properties have led to the demonstration of various perovskite-based devices such as solar cells1, LEDs2-5, photodetectors6 and lasers7,8. Particularly, perovskite solar cells have reached >24% of the energy conversion efficiency and outperformed most of the single-junction thin film solar cells available on the market1. Unfortunately, most of the perovskite-based devices remained more-or-less unstable due to a series of unusual behaviors such as current-voltage hysteresis9 and photo-induced phase segregation10,11. Studies about the underlying mechanisms are in demand. In this dissertation, I focused on studying the charge transport and photoresponse of halide perovskites to reveal the mechanisms related to material stability, particularly under electrical and optical stimuli. The changes of halide perovskite materials in a device under electrical operation were studied by using a microscopic tool, scanning photocurrent microscopy. The results showed the dynamic nature of the doping concentration in the hybrid perovskite CH3NH3PbI3, as a function of the external biasing voltages. Further studies on the synthesis methods showed such a dynamic process could be attributed to electric field-assisted ion migration mainly through defect sites. The partial suppression of ion migration was observed in materials processed at higher temperature. Except the electric-field triggered instability of the internal potential distribution, while under illumination, a different type of stability, the phase stability in mixed-halide perovskites attracted a lot of attention. Phase separation in mixed-halide perovskites under illumination was a tough problem, which directly related to the degradation of desired device performance. In this dissertation, the correlation between the phase stability and morphology was discovered. A model based on thermodynamics was developed to explain such a correlation. Based on the thermodynamic model, the composite materials CsPbX3/Cs4PbX6 with guest-host structures were created with the phase separation problem successfully solved. Furthermore, the composites are sustainably functionalized even under extreme conditions, i.e., under extremely intense illumination, making the composited useful for devices required to work in extreme conditions. The optical and electrical properties of CsPbX3/Cs4PbX6 composites were further investigated for the application of such composites to functional devices. Surprisingly, the presence of the photoluminescence inactive Cs4PbBr6 can significantly enhance the light emitting efficiency of CsPbBr3 in the composites. The unique negative thermal quenching observed near the liquid nitrogen temperature indicates that a type of shallow states generated at the CsPbBr3/Cs4PbBr6 interfaces is responsible for the enhancement of photoluminescence. Finally, light emitting diodes based on CsPbBr3/Cs4PbBr6 composites are demonstrated. Both quantum efficiency and emission brightness are improved significantly compared with similar devices constructed using pure CsPbBr3. The unfavorable charge transport property of host matrix Cs4PbBr6 could be circumvented by optimizing the ratio between the host and the guest components and the total thickness of the composite thin films. The inorganic composition of the emitting layer also leads to improved device stability under the condition of continuous operation. The studies in this dissertation indicated great potentials of composite materials with optimized designed properties. Depends on the application purposes, more matrix materials with the combination of halide perovskites need to be explored. The future plan will more directed to the investigations of fundamental photophysics and charge transport in a large collection of compositing combinations.
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Date Issued: 2019
Identifier: 2019_Summer_Wang_fsu_0071E_15292
Format: Thesis

Title: Developing Multi-Frequency EPR Methods for Studying Protein-Lipid Interactions on the HIV Membrane.
Creator: Hayati, Zahra, Song, Likai, Hill, S. (Stephen Olof), Cross, Timothy A., Bonesteel, N. E., Murphy, Jeremiah Wayne, Florida State University, College of Arts and Sciences,...
Show moreHayati, Zahra, Song, Likai, Hill, S. (Stephen Olof), Cross, Timothy A., Bonesteel, N. E., Murphy, Jeremiah Wayne, Florida State University, College of Arts and Sciences, Department of Physics
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Abstract/Description: Electron paramagnetic resonance (EPR) spectroscopy is a powerful technique to study biomolecules. EPR has been employed to investigate the structure and dynamics of biological membranes, membrane proteins, and protein-lipid interactions. Multi-frequency and high-field experiments enhance the ability of EPR to observe spin dynamics at different time scales and to obtain high-resolution spectra, including 𝑔 anisotropy sensitivity. However, the lack of available techniques and instruments...
Show moreElectron paramagnetic resonance (EPR) spectroscopy is a powerful technique to study biomolecules. EPR has been employed to investigate the structure and dynamics of biological membranes, membrane proteins, and protein-lipid interactions. Multi-frequency and high-field experiments enhance the ability of EPR to observe spin dynamics at different time scales and to obtain high-resolution spectra, including 𝑔 anisotropy sensitivity. However, the lack of available techniques and instruments hinders the application of high-field EPR for biological studies. In this work, we focused on the development of multi-frequency EPR methods in order to characterize protein-lipid interactions on the human immunodeficiency virus (HIV) membrane. HIV infects T cells through a process of membrane fusion. The membrane-bound regions of a viral surface protein gp41, including the membrane proximal ectodomain region (MPER) and the transmembrane region (TM), facilitate membrane fusion and have been targeted for vaccine and drug development. This fusion process is mediated by the raft-like viral membrane that contains a high quantity of cholesterol. The molecular details of gp41-viral membrane interactions during the fusion process are still unclear. To investigate these interactions, we introduced and further developed several EPR methods: 1) Determining peptide-induced lipid orientational disorder using magnetically aligned bicelles (Chapter 3). Bicelles with 20 mol% cholesterol were applied to elucidate how the MPER/TM disrupts the lipid orientational order of the viral membrane. 2) Analyzing the lipid lateral ordering of raft-like lipids using EPR at 94 GHz (Chapter 4). The results demonstrated that this parameter, which reflects the order of the lipids along the membrane plane, has a high sensitivity to lipid motion changes as a result of protein-lipid interactions or lipid composition/position differences. 3) Development of magnetically aligned bicelles containing raft-like lipids using multi-frequency EPR (Chapter 5). For the first time, raft- like bicelles were aligned in the magnetic field with an optimized q value and lipid ratios. These aligned membranes enable studies of membrane properties and protein associations, including the MPER/TM. Other methods involved in this study included lipid fluidity measurements, a fairly new membrane permeability assay, and the application of spin-spin distance measurements to determine peptide self-association and oligomerization. Using these methods, we demonstrated that the MPER interacts strongly with the viral membrane, perturbs the bilayer, and induces significant lipid mobility, membrane permeability, and lipid orientational order changes. The MPER-induced membrane property changes are modulated by the cholesterol content and the TM. Cholesterol inhibits MPER-lipid interactions and promotes MPER/TM oligomerization. The TM stabilizes the MPER on the membrane and abolishes the inhibition effect of cholesterol. In summary, we have improved multi-frequency EPR techniques to study proteins and membranes, and elucidated the mechanism of‎ the‎ MPER/TM‎ of‎ HIV‎ gp41’s‎ interaction with the viral membrane.
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Date Issued: 2019
Identifier: 2019_Fall_Hayati_fsu_0071E_15110
Format: Thesis

Title: Electrical Properties Mapping and Coil Characterization at High Magnetic Fields.
Creator: Amouzandeh, Ghoncheh, Grant, Samuel C., Hill, S. (Stephen Olof), Levenson, Cathy W., Brey, William W., Boebinger, Gregory S., Reina, Laura, Florida State University, College of...
Show moreAmouzandeh, Ghoncheh, Grant, Samuel C., Hill, S. (Stephen Olof), Levenson, Cathy W., Brey, William W., Boebinger, Gregory S., Reina, Laura, Florida State University, College of Arts and Sciences, Department of Physics
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Abstract/Description: Electrical properties (EP), namely conductivity and permittivity, can provide endogenous (having an internal origin) contrast for tissue characterization. EP of the biological tissue are strongly related to essential determinants of the physiological state of tissue such as ionic concentration and mobility, water content and cell structure. As a result, non-invasive measurement of EP has been increasingly used in neuroimaging and other areas. Magnetic resonance electrical property tomography ...
Show moreElectrical properties (EP), namely conductivity and permittivity, can provide endogenous (having an internal origin) contrast for tissue characterization. EP of the biological tissue are strongly related to essential determinants of the physiological state of tissue such as ionic concentration and mobility, water content and cell structure. As a result, non-invasive measurement of EP has been increasingly used in neuroimaging and other areas. Magnetic resonance electrical property tomography (EPT) is a recently introduced technique that can provide maps of EP from conventional MRI data by measuring the distortions induced on the radio frequency (RF) field (B1+). Although its feasibility has been shown at clinical field strengths (1-7T), the application of EPT to routine medical protocols is limited, partly due to reconstruction inaccuracies and variations. In this dissertation, the first application of EPT at 21.1 T (900 MHz), the highest magnetic field available for MRI, is presented with a focus on pre-clinical research. The ultra-high pre-clinical field provides improved signal-to-noise ratios and higher interaction between sample EP and the applied RF field that can enhance EPT accuracy and precision. Helmholtz-based EPT was implemented in its full-form, which demands the complex B1+ field, and a simplified form requiring either just the B1+ field phase for conductivity or the B1+ field magnitude for permittivity. Experiments were conducted at 21.1 T using birdcage and saddle coils operated in linear or quadrature transceive mode, respectively. Feasibility and accuracy of EPT approaches at this field were evaluated using a phantom, ex and in vivo Sprague-Dawley rats under the conditions of naïve and ischemic stroke via transient middle cerebral artery occlusion. Different conductivity reconstruction approaches applied to the phantom displayed average errors of 23-86% to target values. Permittivity reconstructions showed higher agreement and an average 5-8% error to the target depending on the reconstruction approach. The full-form technique generated from the linear birdcage provided the best accuracy for the EP of the phantom. Phase-based conductivity and magnitude-based permittivity mapping provided reasonable estimates but also demonstrated the limitations of Helmholtz-based EPT at 21.1 T. Conductivity and permittivity of ex and in vivo rodent brains also were measured. With the aim to demonstrate the applicability of EPT for ischemic stroke studies, EP of the in vivo rat brain with and without ischemia were measured. The findings demonstrate significantly elevated conductivity and permittivity in the ischemic stroke lesion compared to the contralateral non-pathological side correlated with the increased sodium content and the influx of water intracellularly following ischemia. Permittivity reconstruction was improved significantly over lower fields, suggesting a novel metric for in vivo brain studies. The last section of this dissertation aims to address the implementation of high temperature superconducting (HTS) coils for nuclear magnetic resonance (NMR) spectroscopy with a particular focus on the transmit coil’s characteristics for 13C NMR. NMR is widely used to study the molecular structure and dynamics of molecules in solution, and 13C NMR is critical for structural elucidation in organic chemistry. However, the low sensitivity of NMR has meant that relatively large amounts of the sample or alternate techniques are needed to improve sensitivity. Replacing the normal-metal pickup coils with thin-film HTS resonators has been shown to increase the sensitivity of NMR and reduce the amount of sample required. It also would be convenient and beneficial to use HTS resonators to excite as well as to detect the NMR signal. However, producing a sufficiently strong and rapidly switched excitation field is more challenging with thin-film HTS resonators than with the normal metal coils that they would replace. While double-sided HTS resonators can significantly increase the achievable RF field, the high Q factor of the HTS resonator limits the pulse bandwidth and the minimum dead time following a pulse before reception can begin. This study explored several important aspects of the use of HTS resonators as NMR excitation coils. The presented analysis showed non-linearity in the coil’s response and current compression when high power levels are applied to the coil. Additionally, time domain representation of the excitation pulses generated by the coil showed long ring-up and ring-down times as well as distorted pulse shapes at different power levels. The Fourier transformation of these pulses displayed the limited bandwidth of the coil, which can be problematic for exciting and receiving the whole 13C spectrum. To mitigate the elongated pulse shapes, a shorted stub was added to the transmission path. The result demonstrated improved pulse shapes and reduced phase transients. A similar technique is expected to be applied to the HTS NMR probe to increase the applicability of HTS resonators for transmission.
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Date Issued: 2019
Identifier: 2019_Fall_Amouzandeh_fsu_0071E_15334
Format: Thesis

Title: The Weak Nuclear Form Factor: Nuclear Structure & Coherent Elastic Neutrino-Nucleus Scattering.
Creator: Hernandez, Jesse A. (Jesse Antonio), Piekarewicz, Jorge, Capstick, Simon, Wiedenhoever, Ingo Ludwing M., Florida State University, College of Arts and Sciences, Department of...
Show moreHernandez, Jesse A. (Jesse Antonio), Piekarewicz, Jorge, Capstick, Simon, Wiedenhoever, Ingo Ludwing M., Florida State University, College of Arts and Sciences, Department of Physics
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Abstract/Description: The weak nuclear form factor is the final missing piece to complete our understanding of the nuclear structure and the Coherent Elastic Neutrino Nucleus Scattering (CEvNS) cross section. The weak form factor is dominated by the neutron distributions of the atomic nucleus, which are poorly known. The complex scalar and vector potentials within the nucleus are provided using a Relativistic Mean Field (RMF) approach. These potentials are used to calculate the point neutron and proton...
Show moreThe weak nuclear form factor is the final missing piece to complete our understanding of the nuclear structure and the Coherent Elastic Neutrino Nucleus Scattering (CEvNS) cross section. The weak form factor is dominated by the neutron distributions of the atomic nucleus, which are poorly known. The complex scalar and vector potentials within the nucleus are provided using a Relativistic Mean Field (RMF) approach. These potentials are used to calculate the point neutron and proton distributions, and in conjunction with single-nucleon electric Sachs form factors---obtained from data---are used to predict the weak form factor. It is determined that the radius of the proton distributions agree within 1% to the experimental values. The agreement of the proton distributions gives confidence that the predicted neutron distributions are computed correctly. It is also determined that to constrain the weak form factor, next-generation measurements need to be at 1% error. The correction due to the weak form factor for CEvNS is determined to be approximately between 10-40% for neutron number, N, ranging from 20 to 126. The findings show that the precise measurement of the weak form factor is necessary for the accurate determination of the CEvNS cross section and our comprehension of the nuclear structure as a whole. Most importantly, the predicted quantities and estimated errors give guidance to experiments measuring the weak form factor.
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Date Issued: 2019
Identifier: 2019_Fall_Hernandez_fsu_0071N_15473
Format: Thesis

Title: The Search for N* Resonances: Measurement of Differential Cross Sections and Polarization Observables for γp → pω and γp → K0Σ+ Using Circularly-Polarized Photons at CLAS, Jefferson Lab.
Creator: Akbar, Zulkaida, Crede, Volker, Meyer-Bäse, Anke, Piekarewicz, Jorge, Eugenio, Paul Michael, Adams, Todd, Florida State University, College of Arts and Sciences, Department of...
Show moreAkbar, Zulkaida, Crede, Volker, Meyer-Bäse, Anke, Piekarewicz, Jorge, Eugenio, Paul Michael, Adams, Todd, Florida State University, College of Arts and Sciences, Department of Physics
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Abstract/Description: The study of baryon resonances offers a deeper understanding of the strong interaction, since the dynamics and relevant degrees of freedom hidden within them are reflected by the properties of these states. The baryon resonances have been fairly accurately predicted in the low-energy region by constituent quark models and lattice quantum chromodynamics. However, most of the predicted higher-lying excited resonances (center-of-mass energies above 1.7 GeV/c²) and experimental findings do not...
Show moreThe study of baryon resonances offers a deeper understanding of the strong interaction, since the dynamics and relevant degrees of freedom hidden within them are reflected by the properties of these states. The baryon resonances have been fairly accurately predicted in the low-energy region by constituent quark models and lattice quantum chromodynamics. However, most of the predicted higher-lying excited resonances (center-of-mass energies above 1.7 GeV/c²) and experimental findings do not match up. The model calculations predict more baryon resonances than have been experimentally observed. Quark model calculations have suggested that some of the unobserved resonances couple strongly to γp reactions. The higher-lying excited are also generally predicted to have strong couplings to final states involving a heavier meson, e.g. one of the vector mesons, ρ, ω, ϕ. The excited states of the nucleon are usually found as broadly overlapping resonances, which may decay into a multitude of finasl states involving mesons and baryons. Polarization observables make it possible to isolate singleresonance contributions from other interference terms. This works presents measurements of the helicity asymmetry, E, for the reaction γp → pω in the energy range 1.1 GeV < Eγ < 2.3 GeV, differential cross sections, and spin density matrix elements, also for the reaction γp → pω in the energy range 1.5 GeV < Eγ < 5.4 GeV. Photoproduction of nucleon resonances in their decay to strange particles also offers attractive possibilities because the strange quark in the particle generates another degree of freedom and gives additional information not available from the nucleon-nucleon scattering. Thus, we have also extracted the helicity asymmetry, E, for the reaction γp → K⁰Σ⁺ in the energy range 1.1 GeV < Eγ < 2.1 GeV, differential cross sections, and recoil hyperon polarization, P, also for the reaction γp → K⁰Σ⁺ in the energy range 1.15 GeV < Eγ < 3.0 GeV. The data were collected at Jefferson Lab, using the CLAS detector, as part of the g9a and g12 experiments. Both experiments, as part of the N* spectroscopy program at Jefferson Laboratory, accumulated photoproduction data using circularly-polarized photons incident on a longitudinally-polarized butanol target in the g9a experiment and un-polarized liquid hydrogen target for the g12 experiment. A partial-wave analysis to the E data for the reaction γp → pω within the Bonn-Gatchina framework found dominant contributions from the 3/2⁺ near threshold, which is identified with the sub-treshold N(1720)3/2⁺ resonance. Some additional resonances and the t-channel π and pomeron exchange are needed to describe the data.
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Date Issued: 2018
Identifier: 2018_Su_Akbar_fsu_0071E_14714
Format: Thesis

Title: Scale Setting and Topological Observables in Pure SU(2) LGT.
Creator: Clarke, David A. (David Anthony), Berg, Bernd A., Reina, Laura, Albrecht-Schmitt, Thomas E., Yohay, Rachel, Höflich, Peter, Florida State University, College of Arts and...
Show moreClarke, David A. (David Anthony), Berg, Bernd A., Reina, Laura, Albrecht-Schmitt, Thomas E., Yohay, Rachel, Höflich, Peter, Florida State University, College of Arts and Sciences, Department of Physics
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Abstract/Description: In this dissertation, we investigate the approach of pure SU(2) lattice gauge theory to its continuum limit using the deconfinement temperature, six gradient scales, and six cooling scales. We find that cooling scales exhibit similarly good scaling behavior as gradient scales, while being computationally more efficient. In addition, we estimate systematic error in continuum limit extrapolations of scale ratios by comparing standard scaling to asymptotic scaling. Finally we study topological...
Show moreIn this dissertation, we investigate the approach of pure SU(2) lattice gauge theory to its continuum limit using the deconfinement temperature, six gradient scales, and six cooling scales. We find that cooling scales exhibit similarly good scaling behavior as gradient scales, while being computationally more efficient. In addition, we estimate systematic error in continuum limit extrapolations of scale ratios by comparing standard scaling to asymptotic scaling. Finally we study topological observables in pure SU(2) using cooling to smooth the gauge fields, and investigate the sensitivity of cooling scales to topological charge. We find that large numbers of cooling sweeps lead to metastable charge sectors, without destroying physical instantons, provided the lattice spacing is fine enough and the volume is large enough. Continuum limit estimates of the topological susceptibility are obtained, of which we favor χ 1/4 /T c = 0.643(12). Differences between cooling scales in different topological sectors turn out to be too small to be detectable within our statistical error.
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Date Issued: 2018
Identifier: 2018_Fall_Clarke_fsu_0071E_14832
Format: Thesis

Title: EPR Study of Molecular Qubits Based on Lanthanide Nanomagnets.
Creator: Komijani, Dorsa, Hill, S., Shatruk, Mykhailo, Piekarewicz, Jorge, Van Tol, Johan, Schlottmann, Pedro U., Florida State University, College of Arts and Sciences, Department of...
Show moreKomijani, Dorsa, Hill, S., Shatruk, Mykhailo, Piekarewicz, Jorge, Van Tol, Johan, Schlottmann, Pedro U., Florida State University, College of Arts and Sciences, Department of Physics
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Abstract/Description: Molecular magnets containing one or more open shell elements are one of the proposed systems for quantum information processing that can be chemically engineered to have well-separated and stable quantum states. This dissertation explores mono- and dinuclear lanthanide nanomagnets for quantum information processing and spintronics by means of continuous-wave and pulsed electron paramagnetic resonance (EPR) spectroscopy. EPR is a powerful and sensitive technique that allows us to probe the ﬁne...
Show moreMolecular magnets containing one or more open shell elements are one of the proposed systems for quantum information processing that can be chemically engineered to have well-separated and stable quantum states. This dissertation explores mono- and dinuclear lanthanide nanomagnets for quantum information processing and spintronics by means of continuous-wave and pulsed electron paramagnetic resonance (EPR) spectroscopy. EPR is a powerful and sensitive technique that allows us to probe the ﬁne structure of the ground spin state in molecular magnets. In Chapter 2, we demonstrate that atomic clock transitions (ACTs) can be employed as a means of enhancing the coherence of molecular spin qubits without resorting to extreme dilution, which can be impractical at the stage of device design for multi-qubit gate operations. This approach is illustrated with a holmium molecular nanomagnet in which long coherence times (up to 8.4 microseconds at 5 kelvin) are obtained at unusually high concentrations. ACTs are realized in the vicinity of avoided level crossings within the ground doublet of the holmium compound, at which several sources of decoherence are mitigated. In Chapter 3, we continue the pulsed EPR study presented in Chapter 2 to introduce electro-nuclear atomic clock transitions in a hybrid system with both large electronic and nuclear moment. We demonstrate an enhancement in the coherence time of hybrid transitions that involve coupled dynamics of electron and nuclear spins. This is signiﬁcant for applications in hybrid magnetic qubits, where manipulation of the nuclear spin is controlled by EPR pulses. In Chapter 4, we report single-crystal and powder high-ﬁeld EPR (HF-EPR) measurements on a neutral [TbPc2]0 complex for which the organic bis-phthalocyaninato (Pc2) ligand is open shell, i.e., it carries an unpaired electron. A highly anisotropic EPR signal can be attributed to the radical, suggesting an appreciable interaction with the Ising-like Tb(III) ion. Analysis of the results unambiguously demonstrate that the radical-Tb(III) coupling is due to a ferromagnetic exchange interaction. The essential physics is captured via an eﬀective spin Hamiltonian in which the exchange is assumed to be isotropic, while the magnetic anisotropy is folded entirely into the single-ion properties of the terbium ion. In Chapter 4, we investigate lanthanide-radical interactions across the lanthanide (Ln) series in double-decker compounds (LnPc2). We further discuss the eﬀect of free ion anisotropy on the magnetic properties of the lanthanide ion and the exchange coupled radical. Finally, in Chapter 6, we present HF-EPR studies of a series of symmetric and asymmetric triple-decker compounds that are potential candidates for two-qubit gate operations. Triple-decker compounds contain two lanthanide ions in each molecule that are linked by a phthalocyanine (Pc) ring sandwiched by Pc or porphyrin on the top and bottom. We further show that the two inequivalent sites required for two-qubit gates can be chemically engineered by adjusting the coordination symmetry for one of the ions in these dinuclear compounds.
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Date Issued: 2018
Identifier: 2018_Su_Komijani_fsu_0071E_14626
Format: Thesis

Title: Experimental Investigations of Mass-7 Destruction in Deuteron Induced Reactions with Respect to Standard Big Bang Nucleosynthesis.
Creator: Rijal, Nabin, Weidenhoever, Ingo Ludwing M., Humayun, Munir, Volya, Alexander, Höflich, Peter, Almaraz-Calderon, Sergio J., Florida State University, College of Arts and...
Show moreRijal, Nabin, Weidenhoever, Ingo Ludwing M., Humayun, Munir, Volya, Alexander, Höflich, Peter, Almaraz-Calderon, Sergio J., Florida State University, College of Arts and Sciences, Department of Physics
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Abstract/Description: The Big-Bang theory is the most widely accepted description of the origin of the Universe, creating elementary particles and synthesizing light nuclei up to mass-7 within the first few minutes of the Big-Bang. Its parameters have been recently precisely determined through he multi-years WMAP (Wilkinson Microwave Anisotropy Probe, NASA mission) followed by Planck (ESA mission). These results tightly constrain the baryonic density in the Universe with the highest precision ever achieved,...
Show moreThe Big-Bang theory is the most widely accepted description of the origin of the Universe, creating elementary particles and synthesizing light nuclei up to mass-7 within the first few minutes of the Big-Bang. Its parameters have been recently precisely determined through he multi-years WMAP (Wilkinson Microwave Anisotropy Probe, NASA mission) followed by Planck (ESA mission). These results tightly constrain the baryonic density in the Universe with the highest precision ever achieved, resulting in more constraints in the light element abundance predicted in the Standard Big Bang Nucleosynthesis (SBBN). The observed amount of all other light elements (H, D, 3He, 4He) agrees well with the SBBN calculation but the 7Li is overpredicted by a factor of 3 − 4, which is referred as the Primordial Lithium Problem. The Lithium problem is the disagreement in the theoretical and observed amount of 7Li in the Cosmos which has the key importance in the Big Bang Nucleosynthesis theory which can’t be explained by uncertainties in the main reactions included in the SBBN. In this work, we performed experiments on certain nuclear reactions, 7Be + d and 7Li + d, at energies relevant to SBBN, which could destroy a fraction of the mass-7 nuclei in the conditions of the Big Bang and could offer an explanation of the observed deviation from the prediction of SBBN. In preparation for the main experiment of this dissertation 7Be+d -> p+2 alpha, we performed an experiment for mirror nuclear reaction 7Li + d -> n + 2 alpha, with ANASEN in gas target mode using deuterium as an active gas target and detected 2 -particles in coincidence. In particular, we investigated the 7Be+d reaction at SBBN energies using a radioactive 7Be beam and deuterium gas target, stopping the beam in the target gas inside the ANASEN (Array for Nuclear Astrophysics and Structures with Exotic Nuclei) detector at the Florida State University (FSU). ANASEN is an active target detector system which tracks the charged particles with cylindrical configuration of a position sensitive proportional counter, a Silicon detector array backed up by Caesium Iodide (CsI) detectors; one of the first detectors of its kind. The experiment measured a continuous excitation function by slowing down the beam particles in the target gas down to very low energies into the Gamow window. Our experimental set-up provided a high detection efficiency for all relevant reaction channels focusing on the lowest energies, relevant to the Big Bang Nucleosynthesis (BBN). Results of these experiments after a comprehensive data analysis are documented in this dissertation.
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Date Issued: 2018
Identifier: 2018_Su_RIJAL_fsu_0071E_14658
Format: Thesis

Title: Direct Observation of Structural Defects in Pyrochlore Yb₂Ti₂O₇ by Atomic Resolution Scanning Transmission Electron Microscopy.
Creator: Shafieizadeh, Zahra, Xin, Yan, Chiorescu, Irinel, Andrei, Petru, Reina, Laura, Van Winkle, David H., Florida State University, College of Arts and Sciences, Department of Physics
Abstract/Description: In transition metal oxides, such as A2B2O7, the B-site cations typically govern many of the fundamentally and technologically interesting properties. The cubic pyrochlore oxides, A2B2O7, have attracted much attention over the past 20 years. However, even after years of theoretical and experimental study of pyrochlore compounds many fundamental questions still remain about the nature of the magnetic ground states in this series. In the pyrochlore structure, both the rare earth and the...
Show moreIn transition metal oxides, such as A2B2O7, the B-site cations typically govern many of the fundamentally and technologically interesting properties. The cubic pyrochlore oxides, A2B2O7, have attracted much attention over the past 20 years. However, even after years of theoretical and experimental study of pyrochlore compounds many fundamental questions still remain about the nature of the magnetic ground states in this series. In the pyrochlore structure, both the rare earth and the transition metal sublattices have a topology consisting of corner-sharing tetrahedra and are, thus, geometrically frustrated. Yb2Ti2O7 is part of a series of compounds called the rare-earth titanates. It’s been noticed that its magnetic ground states are sample dependent and shows broad specific heat peak in colored single crystals. It could have long-range ordered collinear ferromagnetic state, or non-collinear ferromagnetic fluctuations, or short ranged fluctuations. Atomic resolution high-angle-annular-dark-field STEM (HAADF-STEM) imaging is a powerful tool to observe and obtain information on defect structures. The primary aim of this thesis is, therefore, to study defects in Yb2Ti2O7 samples by quantitative scanning transmission electron microscopy at atomic resolution. We study three types of samples, polycrystalline sample and yellowish single crystal grown by conventional floating zone (FZ) method and high quality colorless single crystal grown by the traveling solvent floating zone (TSFZ) technique. We compared the atomic structure of them using STEM and found different types of defects: Yb atoms “stuffing” into Ti sites, extended defects such as anti-phase boundaries (APB) and dissociated superdislocations and grain boundary defects were discovered for the first time and found to be prevalent in the yellowish single crystal grown by FZ, contrary to the few found in high quality colorless transparent single crystals or stoichiometric white polycrystalline samples. These results are discussed along with the results from simulation. Also, EELS results showed that the Ti valence was not decreased in defected areas and its value is 4+. These results explain the varied magnetic properties and broad specific heat peak of yellowish Yb2Ti2O7 single crystals grown by conventional FZ method and provide new insights into understanding the roles of defects on physical properties of the geometrically frustrated pyrochlore compounds.
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Date Issued: 2018
Identifier: 2018_Su_Shafieizadeh_fsu_0071E_14721
Format: Thesis

Title: Exploring the Nuclear Structure of the A = 39 Isobars.
Creator: Abromeit, Brittany Lynn, Tabor, Samuel L., Humayun, Munir, Hsiao, Eric Y., Riley, Mark A., Volya, Alexander, Florida State University, College of Arts and Sciences, Department...
Show moreAbromeit, Brittany Lynn, Tabor, Samuel L., Humayun, Munir, Hsiao, Eric Y., Riley, Mark A., Volya, Alexander, Florida State University, College of Arts and Sciences, Department of Physics
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Abstract/Description: Investigation of nuclei with neutron and proton imbalance is at the forefront of nuclear physics research today, along with how the nuclear structure varies with the movement of the nucleons. Experimental data and theoretical models work hand-in-hand to understand the structure of these nuclei. Two of the A = 39 isobars, residing in limbo between the sd- and fp-shells are the isotopes of interest for this study. With 24 neutrons, eight neutrons more than the stable isotope of phosphorous, ³⁹P...
Show moreInvestigation of nuclei with neutron and proton imbalance is at the forefront of nuclear physics research today, along with how the nuclear structure varies with the movement of the nucleons. Experimental data and theoretical models work hand-in-hand to understand the structure of these nuclei. Two of the A = 39 isobars, residing in limbo between the sd- and fp-shells are the isotopes of interest for this study. With 24 neutrons, eight neutrons more than the stable isotope of phosphorous, ³⁹P is considered a neutron-rich exotic nucleus, one of which has not been extensively studied until now. Since the late 1990s only two experiments have been conducted, producing the three known gamma-rays and one tentative gamma-ray for ³⁹P. Except for half-life measurements and mass measurements, no further studies of ³⁹P have been done prior to a beta-gamma coincidence experiment conducted in this study at the National Superconducting Cyclotron Laboratory (NSCL) using the Beta Counting System. Continuing up the isobaric chain from ³⁹P toward stability, ³⁹Ar is reached. Unlike ³⁹P, ³⁹Ar is nested between two of the stable isotopes of argon. Being closer to stability, it has been studied more extensively using transfer reactions, however, limited information on high-spin states is produced from only two prior experiments. Despite the more extensive study of ³⁹Ar, the observed gamma transitions are only well known for low-spin states except for one band of high-spin states which have been studied heavily using the gamma spectroscopy setup at the John D. Fox Superconducting Linear Accelerator Laboratory at Florida State University. Results for both isotopes, along with comparisons to Shell Model calculations will be presented.
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Date Issued: 2018
Identifier: 2018_Fall_Abromeit_fsu_0071E_14900
Format: Thesis

Title: Structural Stability and Emergent Phases in Oxygen Deficient Complex Transition Metal Oxides.
Creator: Ghosh, Soham S., Manousakis, Efstratios, Shatruk, Mykhailo, Bonesteel, N. E., Roberts, Winston, Van Winkle, David, Flaherty, Francis A., Florida State University, College of...
Show moreGhosh, Soham S., Manousakis, Efstratios, Shatruk, Mykhailo, Bonesteel, N. E., Roberts, Winston, Van Winkle, David, Flaherty, Francis A., Florida State University, College of Arts and Sciences, Department of Physics
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Abstract/Description: This dissertation is a theoretical and computational examination of structural, electronic and magnetic properties of complex transition metal oxide structures. Our work is motivated by experimental observations that transition metal oxides manifest novel properties at surfaces and interfaces that are absent in bulk, and that there exist competing ground states driven by off-stoichiometry, oxygen vacancy and reduction of symmetry. We examine these properties using density functional theory ...
Show moreThis dissertation is a theoretical and computational examination of structural, electronic and magnetic properties of complex transition metal oxide structures. Our work is motivated by experimental observations that transition metal oxides manifest novel properties at surfaces and interfaces that are absent in bulk, and that there exist competing ground states driven by off-stoichiometry, oxygen vacancy and reduction of symmetry. We examine these properties using density functional theory (DFT) within the spin-generalized gradient approximation (Spin-GGA) along with the application of a Hubbard U (GGA + U). We present our detailed results for the following systems: oxygen deficient strontium titanate surface, strontium ruthenate interfaced with ruthenium metal inclusions, and ytterbium titanate with Yb "stuffing". In the course of our work, we cover materials with 3d, 4d and 4f band characters, each of which have different band masses, electron-electron correlations and spin-orbit coupling (SOC) strength. We investigate the role of surface termination, oxygen vacancy doping and cation "stuffing" defects in these metal-oxides and show the emergence of novel properties consistent with experimentally acquired information and possible applications. We conclude by presenting implications for further work.
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Date Issued: 2017
Identifier: FSU_SUMMER2017_Ghosh_fsu_0071E_13962
Format: Thesis

Title: Mott Transition in Strongly Correlated Materials: Many-Body Methods and Realistic Materials Simulations.
Creator: Lee, Tsung-Han, Dobrosavljević, Vladimir, Dalal, Naresh S., Manousakis, Efstratios, Balicas, Luis, Piekarewicz, Jorge, Florida State University, College of Arts and Sciences,...
Show moreLee, Tsung-Han, Dobrosavljević, Vladimir, Dalal, Naresh S., Manousakis, Efstratios, Balicas, Luis, Piekarewicz, Jorge, Florida State University, College of Arts and Sciences, Department of Physics
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Abstract/Description: Strongly correlated materials are a class of materials that cannot be properly described by the Density Functional Theory (DFT), which is a single-particle approximation to the original many-body electronic Hamiltonian. These systems contain d or f orbital electrons, i.e., transition metals, actinides, and lanthanides compounds, for which the electron-electron interaction (correlation) effects are too strong to be described by the single-particle approximation of DFT. Therefore, complementary...
Show moreStrongly correlated materials are a class of materials that cannot be properly described by the Density Functional Theory (DFT), which is a single-particle approximation to the original many-body electronic Hamiltonian. These systems contain d or f orbital electrons, i.e., transition metals, actinides, and lanthanides compounds, for which the electron-electron interaction (correlation) effects are too strong to be described by the single-particle approximation of DFT. Therefore, complementary many-body methods have been developed, at the model Hamiltonians level, to describe these strong correlation effects. Dynamical Mean Field Theory (DMFT) and Rotationally Invariant Slave-Boson (RISB) approaches are two successful methods that can capture the correlation effects for a broad interaction strength. However, these many-body methods, as applied to model Hamiltonians, treat the electronic structure of realistic materials in a phenomenological fashion, which only allow to describe their properties qualitatively. Consequently, the combination of DFT and many body methods, e.g., Local Density Approximation augmented by RISB and DMFT (LDA+RISB and LDA+DMFT), have been recently proposed to combine the advantages of both methods into a quantitative tool to analyze strongly correlated systems. In this dissertation, we studied the possible improvements of these approaches, and tested their accuracy on realistic materials. This dissertation is separated into two parts. In the first part, we studied the extension of DMFT and RISB in three directions. First, we extended DMFT framework to investigate the behavior of the domain wall structure in metal-Mott insulator coexistence regime by studying the unstable solution describing the domain wall. We found that this solution, differing qualitatively from both the metallic and the insulating solutions, displays an insulating-like behavior in resistivity while carrying a weak metallic character in its electronic structure. Second, we improved DMFT to describe a Mott insulator containing spin-propagating and chargeless fermionic excitations, spinons. We found the spinon Fermi-liquid, in the Mott insulating phase, is immiscible to the electron Fermi-liquid, in the metallic phase, due to the strong scattering between spinons in a metal. Third, we proposed a new approach within the slave-boson (Gutzwiller) framework that allows to describe both the low energy quasiparticle excitation and the high energy Hubbard excitation, which cannot be captured within the original slave-boson framework. In the second part, we applied LDA+RISB to realistic materials modeling. First, we tested the accuracy of LDA+RISB on predicting the structure of transition metal compounds, CrO, MnO, FeO, CoO, CoS, and CoSe. Our results display remarkable agreements with the experimental observations. Second, we applied LDA+RISB to analyze the nature of the Am-O chemical bonding in the CsAm(CrO_4)_2 crystal. Our results indicate the Am-O bonding has strongly covalent character, and they also address the importance of the correlation effects to describe the experimentally observed electronic structure. In summary, we proposed three extensions within DMFT and RISB framework, which allow to investigate the domain wall structure in metal-Mott insulator coexistence regime, the metal-to-Mott-insulator transition with spinons excitation in the Mott-insulating phase, and the Hubbard excitation within RISB approach. Furthermore, we demonstrated that LDA+RISB is a reliable approximation to the strongly correlated materials by applying it to the transition metal compounds and the Americian chromate compounds.
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Date Issued: 2017
Identifier: FSU_SUMMER2017_Lee_fsu_0071E_13983
Format: Thesis

Title: Sensitive Spin Detection Using an on-Chip Squid-Waveguide Resonator.
Creator: Yue, Guang, Chiorescu, Irinel, Dalal, Naresh S., Reina, Laura, Schlottmann, Pedro U., Xiong, Peng, Florida State University, College of Arts Sciences, Department of Physics
Abstract/Description: Quantum computing gives novel way of computing using quantum mechanics, which furthers human knowledge and has exciting applications. Quantum systems with diluted spins such as rare earth ions hosted in single crystal, molecule-based magnets etc. are promising qubits candidates to form the basis of a quantum computer. High sensitivity measurement and coherent control of these spin systems are crucial for their practical usage as qubits. The micro-SQUID (direct-current micrometer-sized...
Show moreQuantum computing gives novel way of computing using quantum mechanics, which furthers human knowledge and has exciting applications. Quantum systems with diluted spins such as rare earth ions hosted in single crystal, molecule-based magnets etc. are promising qubits candidates to form the basis of a quantum computer. High sensitivity measurement and coherent control of these spin systems are crucial for their practical usage as qubits. The micro-SQUID (direct-current micrometer-sized Superconducting QUantum Interference Device) is capable to measure magnetization of spin system with high sensitivity. For example, the micro-SQUID technique can measure magnetic moments as small as several thousand μB as shown by the study of [W. Wernsdorfer, Supercond. Sci. Technol. 22, 064013 (2009)]. Here we develop a novel on-chip setup that combines the micro-SQUID sensitivity with microwave excitation. Such setup can be used for electron spin resonance measurements or coherent control of spins utilizing the high sensitivity of micro-SQUID for signal detection. To build the setup, we studied the fabrication process of the micro-SQUID, which is made of weak-linked Josephson junctions. The SQUID as a detector is integrated on the same chip with a shorted coplanar waveguide, so that the microwave pulses can be applied through the waveguide to excite the sample for resonance measurements. The whole device is plasma etched from a thin (∼20nm) niobium film, so that the SQUID can work at in large in-plane magnetic fields of several tesla. In addition, computer simulations are done to find the best design of the waveguide such that the microwave excitation field is sufficiently strong and uniformly applied to the sample. The magnetization curve of Mn₁₂ molecule-based magnet sample is measured to prove the proper working of the micro-SQUID. Electron spin resonance measurement is done on the setup for gadolinium ions diluted in a CaWO₄ single crystal. The measurement shows clear evidence of the resonance signal from the 1st transition of the gadolinium ions' energy levels, which shows the setup is successfully built. Due to the high sensitivity of micro-SQUID and the ability to concentrate microwave energy in small areas of the chip, this setup can detect signals from a small number of spins (10⁷) in a small volume (several μm³).
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Date Issued: 2017
Identifier: FSU_SUMMER2017_Yue_fsu_0071E_13872
Format: Thesis

Title: Tuning the Photoluminescence of Halide Perovskites.
Creator: Knox, Javon M., Gao, Hanwei, Bonesteel, N. E., Van Winkle, David, Florida State University, College of Arts and Sciences, Department of Physics
Abstract/Description: Wavelength tunability or bandgap tuning of mixed halide perovskite, CsPb(IxBry)3 (y=1-x), can be achieved by changing the composition of iodide and bromide ions but under continuous illumination the photoluminescence (PL) peak position shifts from its initial position. This optical instability is attributed to phase segregation, where until photoexcitation the mixed halide anions migrate to iodide-rich and bromide-rich domains. Recent work has shown PL peak stability for mixed halide...
Show moreWavelength tunability or bandgap tuning of mixed halide perovskite, CsPb(IxBry)3 (y=1-x), can be achieved by changing the composition of iodide and bromide ions but under continuous illumination the photoluminescence (PL) peak position shifts from its initial position. This optical instability is attributed to phase segregation, where until photoexcitation the mixed halide anions migrate to iodide-rich and bromide-rich domains. Recent work has shown PL peak stability for mixed halide composition x > 0.6, however this limits the range of tunability to wavelengths greater than 640 nanometers (nm). Here we create a dual-source vapor-evaporation method to create mixed halide which can suppress the phase segregation and improve the photoluminescence stability.
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Date Issued: 2017
Identifier: FSU_SUMMER2017_Knox_fsu_0071N_14120
Format: Thesis

Title: Surface Modification for Improved Design and Functionality of Nanostructured Materials and Devices.
Creator: Keiper, Timothy David, Xiong, Peng, Chase, P. Bryant, van Winkle, David H., Rikvold, Per Arne, Riley, Mark A., Florida State University, College of Arts and Sciences, Department...
Show moreKeiper, Timothy David, Xiong, Peng, Chase, P. Bryant, van Winkle, David H., Rikvold, Per Arne, Riley, Mark A., Florida State University, College of Arts and Sciences, Department of Physics
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Abstract/Description: Progress in nanotechnology is trending towards applications which require the integration of soft (organic or biological) and hard (semiconductor or metallic) materials. Many applications for functional nanomaterials are currently being explored, including chemical and biological sensors, flexible electronics, molecular electronics, etc., with researchers aiming to develop new paradigms of nanoelectronics through manipulation of the physical properties by surface treatments. This dissertation...
Show moreProgress in nanotechnology is trending towards applications which require the integration of soft (organic or biological) and hard (semiconductor or metallic) materials. Many applications for functional nanomaterials are currently being explored, including chemical and biological sensors, flexible electronics, molecular electronics, etc., with researchers aiming to develop new paradigms of nanoelectronics through manipulation of the physical properties by surface treatments. This dissertation focuses on two surface modification techniques important for integration of hard and soft materials: thermal annealing and molecular modification of semiconductors. First, the effects of thermal annealing are investigated directly for their implication in the fundamental understanding of transparent conducting oxides with respect to low resistivity contacts for electronic and optoelectronic applications and the response to environmental stimuli for sensing applications. The second focus of this dissertation covers two aspects of the importance of molecular modification on semiconductor systems. The first of these is the formation of self-assembled monolayers in patterned arrays which leads explicitly to the directed self-assembly of nanostructures. The second aspect concerns the modification of the underlying magnetic properties of the preeminent dilute magnetic semiconductor, manganese-doped gallium arsenide. Tin oxide belongs to a class of materials known as transparent conducting oxides which have received extensive interest due to their sensitivity to environmental stimuli and their potential application in transparent and flexible electronics. Nanostructures composed of SnO2 have been demonstrated as an advantageous material for high performance, point-of-care nanoelectronic sensors, capable of detecting and distinguishing gaseous or biomolecular interactions on unprecedented fast timescales. Through bottom-up fabrication techniques, binary oxide nanobelts synthesized through catalyst-free physical vapor deposition are implemented in the field-effect transistor structure. We have discovered that conductivity is absent in as-grown devices. However, utilizing a process for thermal treatment in vacuum and oxygen environments is found to be instrumental in fabricating field-effect transistors with significant conductivity, up to five orders of magnitude above the as-grown devices, for field-effect transistor application. Further investigation by photoluminescence coupled with the annealing parameters reveals that the likely cause of conductance comes from the reduction of surface defect states in the material. Importantly, the annealed material maintains its response to an applied gate potential showing orders of magnitude switching from the 'off' to the 'on' state. In order to show the practical relevance of our improvements on the SnO₂ material, we show our results for implementing the annealed material in biomolecular sensing experiments to detect the presence of streptavidin and Hepatitis C virus. Surface modification was carried out on oxide-free gallium arsenide (in some cases doped with manganese or zinc) through self-assembly of thiol molecules. First, we investigate the ability to pattern via two complementary micro- and nanopatterning techniques, microcontact printing (μCP) and dip-pen nanolithography (DPN). DPN is a unique lithography tool that allows drawing of arbitrary patterns with a molecular ink on a complementary substrate. It is extremely useful in integration of molecular inks within a pre-defined structure. Here, DPN was used to investigate the diffusion of organic molecules from a point source for both a moving and stationary tip on oxide-free GaAs. The diffusion can be calibrated so that intricate patterns down to tens of nanometers can be arbitrarily drawn on the surface. μCP, a less complicated method for large-scale arrayed patterning, is utilized to investigate the deposition of different thiolated molecular inks on GaAs and (Ga,Mn)As. The patterns deposited by μCP provide the template for directed self-assembly of gold nanoparticles. The systems based on these techniques can be extended to many substrate-molecule-nanostructure systems for an incredible variety of applications. Finally, the thiol-(Ga,Mn)As system is studied to determine the effects of molecular modification on the substrates' magnetic properties via modulation of the hole concentration in the wafer. The results for two molecules, one an electron donor and one an electron acceptor, show opposite trends for modulation of both the Curie temperature and the saturation magnetization. We suggest that nanopatterning of electron donor or electron acceptor molecules could lead to the development of reconfigurable nanomagnetic systems in (Ga,Mn)As with potential applications in molecular spintronics or magnetic memory.
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Date Issued: 2017
Identifier: FSU_2017SP_Keiper_fsu_0071E_13728
Format: Thesis

Title: ΛC Semileptonic Decays in a Quark Model.
Creator: Hussain, Md Mozammel, Roberts, Winston, Goldsby, Kenneth A,, Volya, Alexander, Crede, Volker, Owens, Joseph F., Florida State University, College of Arts and Sciences,...
Show moreHussain, Md Mozammel, Roberts, Winston, Goldsby, Kenneth A,, Volya, Alexander, Crede, Volker, Owens, Joseph F., Florida State University, College of Arts and Sciences, Department of Physics
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Abstract/Description: Hadronic form factors for semileptonic decay of the Λ[subscript c] are calculated in a nonrelativistic quark model. The full quark model wave functions are employed to numerically calculate the form factors to all orders in (1/m[subscript c], 1/m[subscript s]). The form factors satisfy relationships expected from the heavy quark effective theory (HQET) form factors. No other semileptonic decays of Λ[subscript c] has been reported other than the decay to the ground state Λ that implies f = B(Λ...
Show moreHadronic form factors for semileptonic decay of the Λ[subscript c] are calculated in a nonrelativistic quark model. The full quark model wave functions are employed to numerically calculate the form factors to all orders in (1/m[subscript c], 1/m[subscript s]). The form factors satisfy relationships expected from the heavy quark effective theory (HQET) form factors. No other semileptonic decays of Λ[subscript c] has been reported other than the decay to the ground state Λ that implies f = B(Λ[subscript c]⁺ → Λl⁺ν[subscript l])/B(Λ[subscript c]⁺ → X[subscript s]l⁺ν[subscript l]) = 1. In this work, the differential decay rates and branching fractions are calculated for transitions to the ground state and a number of excited states of Λ. The branching fraction of the semileptonic decay width to the total width of Λ[subscript c] has been calculated and compared with other theoretical estimates and experimental results. The branching fractions for Λ[subscript c] → Λ*l⁺ν[subscript l] → Σπl⁺ν[subscript l] and Λ[subscript c] → Λ*l⁺ν[subscript l] → NǨl⁺ν[subscript l] are also calculated. Apart from decays to the ground state Λ(1115), it is found that decays through the Λ(1405) provide a significant portion of the branching fraction Λ[subscript c] → X[subscript s]lν[subscript l]. There are various conjectures on the structure of the Λ(1405) while we treated it as a three quark state. A new estimate for f = B(Λ[subscript c]⁺ → Λl⁺ν[subscript l] is obtained.
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Date Issued: 2017
Identifier: FSU_2017SP_Hussain_fsu_0071E_13920
Format: Thesis

Title: The Impact of Microstructure on an Accurate Snow Scattering Parameterization at Microwave Wavelengths.
Creator: Honeyager, Ryan Erick, Liu, Guosheng, Gunzburger, Max D., Ahlquist, Jon E., Ellingson, R. G., Wu, Zhaohua, Florida State University, College of Arts and Sciences, Department of...
Show moreHoneyager, Ryan Erick, Liu, Guosheng, Gunzburger, Max D., Ahlquist, Jon E., Ellingson, R. G., Wu, Zhaohua, Florida State University, College of Arts and Sciences, Department of Earth, Ocean and Atmospheric Science
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Abstract/Description: High frequency microwave instruments are increasingly used to observe ice clouds and snow. These instruments are significantly more sensitive than conventional precipitation radar. This is ideal for analyzing ice-bearing clouds, for ice particles are tenuously distributed and have effective densities that are far less than liquid water. However, at shorter wavelengths, the electromagnetic response of ice particles is no longer solely dependent on particle mass. The shape of the ice particles...
Show moreHigh frequency microwave instruments are increasingly used to observe ice clouds and snow. These instruments are significantly more sensitive than conventional precipitation radar. This is ideal for analyzing ice-bearing clouds, for ice particles are tenuously distributed and have effective densities that are far less than liquid water. However, at shorter wavelengths, the electromagnetic response of ice particles is no longer solely dependent on particle mass. The shape of the ice particles also plays a significant role. Thus, in order to understand the observations of high frequency microwave radars and radiometers, it is essential to model the scattering properties of snowflakes correctly. Several research groups have proposed detailed models of snow aggregation. These particle models are coupled with computer codes that determine the particles' electromagnetic properties. However, there is a discrepancy between the particle model outputs and the requirements of the electromagnetic models. Snowflakes have countless variations in structure, but we also know that physically similar snowflakes scatter light in much the same manner. Structurally exact electromagnetic models, such as the discrete dipole approximation (DDA), require a high degree of structural resolution. Such methods are slow, spending considerable time processing redundant (i.e. useless) information. Conversely, when using techniques that incorporate too little structural information, the resultant radiative properties are not physically realistic. Then, we ask the question, what features are most important in determining scattering? This dissertation develops a general technique that can quickly parameterize the important structural aspects that determine the scattering of many diverse snowflake morphologies. A Voronoi bounding neighbor algorithm is first employed to decompose aggregates into well-defined interior and surface regions. The sensitivity of scattering to interior randomization is then examined. The loss of interior structure is found to have a negligible impact on scattering cross sections, and backscatter is lowered by approximately five percent. This establishes that detailed knowledge of interior structure is not necessary when modeling scattering behavior, and it also provides support for using an effective medium approximation to describe the interiors of snow aggregates. The Voronoi diagram-based technique enables the almost trivial determination of the effective density of this medium. A bounding neighbor algorithm is then used to establish a greatly improved approximation of scattering by equivalent spheroids. This algorithm is then used to posit a Voronoi diagram-based definition of effective density approach, which is used in concert with the T-matrix method to determine single-scattering cross sections. The resulting backscatters are found to reasonably match those of the DDA over frequencies from 10.65 to 183.31 GHz and particle sizes from a few hundred micrometers to nine millimeters in length. Integrated error in backscatter versus DDA is found to be within 25% at 94 GHz. Errors in scattering cross-sections and asymmetry parameters are likewise small. The observed cross-sectional errors are much smaller than the differences observed among different particle models. This represents a significant improvement over established techniques, and it demonstrates that the radiative properties of dense aggregate snowflakes may be adequately represented by equal-mass homogeneous spheroids. The present results can be used to supplement retrieval algorithms used by CloudSat, EarthCARE, Galileo, GPM and SWACR radars. The ability to predict the full range of scattering properties is potentially also useful for other particle regimes where a compact particle approximation is applicable.
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Date Issued: 2017
Identifier: FSU_2017SP_Honeyager_fsu_0071E_13726
Format: Thesis

Title: Automated One-Loop QCD and Electroweak Calculations with NLOX.
Creator: Honeywell, Steven Joseph, Reina, Laura, Aluffi, Paolo, Owens, Joseph F., Roberts, Winston, Yohay, Rachel, Florida State University, College of Arts and Sciences, Department of...
Show moreHoneywell, Steven Joseph, Reina, Laura, Aluffi, Paolo, Owens, Joseph F., Roberts, Winston, Yohay, Rachel, Florida State University, College of Arts and Sciences, Department of Physics
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Abstract/Description: We introduce a new framework, NLOX, in which one-loop QCD and electroweak corrections to Standard Model processes can be automatically calculated. Within this framework, we calculate the first order of electroweak corrections to the hadronic production of Z + 1b-jet and discuss some of the most relevant theoretical issues related to this process.
Date Issued: 2017
Identifier: FSU_2017SP_Honeywell_fsu_0071E_13868
Format: Thesis

Title: Search for Heavy Stable Charged Particles √ at S = 13 TeV Utilizing a Multivariate Approach.
Creator: Ackert, Andrew Kenjiro, Adams, Todd, Magnan, Jerry F., Prosper, Harrison B., Owens, Joseph F., Piekarewicz, Jorge, Florida State University, College of Arts and Sciences,...
Show moreAckert, Andrew Kenjiro, Adams, Todd, Magnan, Jerry F., Prosper, Harrison B., Owens, Joseph F., Piekarewicz, Jorge, Florida State University, College of Arts and Sciences, Department of Physics
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Abstract/Description: Heavy stable charged particles (HSCPs) have been searched for at the Large Hadron Collider since its initial data taking in 2010. The search for heavy stable charged particles provide a means of directly probing the new physics realm, as they produce a detector signature unlike any particle discovered to date. The goal of this research is to investigate an idea that was introduced in the later stages of 2010-2012 data taking period. Rather than utilizing the current tight selection on the...
Show moreHeavy stable charged particles (HSCPs) have been searched for at the Large Hadron Collider since its initial data taking in 2010. The search for heavy stable charged particles provide a means of directly probing the new physics realm, as they produce a detector signature unlike any particle discovered to date. The goal of this research is to investigate an idea that was introduced in the later stages of 2010-2012 data taking period. Rather than utilizing the current tight selection on the calculated particle mass the hypothesis is that by incorporating a multivariate approach, specifically an artificial neural network, the remaining selection criteria could be loosened allowing for a greater signal acceptance while maintaining acceptable background rejection via the multivariate discriminator from the artificial neural network. The increase in signal acceptance and retention or increase in background rejection increases the discovery potential for HSCPs and as a secondary objective calculates improved limits on the HSCP signal models. The multivariate approach was developed and tested using 2.5 fb⁻¹ of 2015 data at √s = 13 TeV based on both the past tracker-only and Tracker+TOF HSCP analyses. The multivariate analyses were able to produce improved upper cross section limits on both expected and observed cross sections compared to the past 2015 results. The lower mass limits produced by the multivariate analyses are also improved, but the improvement was found to be less than 5% higher compared to the past 2015 HSCP search results. A final comparison of the multivariate approach to past HSCP searches was conducted on 12.9 fbfb⁻¹ of 2016 data at √s = 13 TeV. No statistically significant excess of data over background prediction is observed. Therefore no evidence of HSCPs is claimed. The tracker-only (Tracker+TOF) multivariate analysis produced lower mass limits of 1870 (1820) GeV for gluinos with 10% R-hadrons produced neutral, 1260 (1210) GeV for stops, 680 (670) GeV for decay-product staus, 340 (370) GeV for directly pair-produced staus, 720 (750) GeV for modified Drell-Yan |Q| = 1e, and 700 (900) GeV for modified Drell-Yan |Q| = 2e. Overall, the multivariate approach produced improved lower mass limits compared to the results from the past 2016 HSCP search. The overall improvements in cross section and mass limits using the multivariate approach produced the best limits on HSCPs to date. Furthermore the multivariate approach is shown as a viable method of searching for HSCPs. With the HSCP search covering a broad range of beyond the Standard Model physics, the lack of evidence and subsequent limits produced place important restrictions on the theoretical models that predict HSCPs.
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Date Issued: 2017
Identifier: FSU_2017SP_Ackert_fsu_0071E_13836
Format: Thesis

Title: Computational Studies of Magnetically Doped Semiconductor Nanoclusters.
Creator: Gutsev, Lavrenty Gennady, Dalal, Naresh S., Chiorescu, Irinel, Strouse, Geoffrey F., Yang, Wei, Florida State University, College of Arts and Sciences, Department of Chemistry &...
Show moreGutsev, Lavrenty Gennady, Dalal, Naresh S., Chiorescu, Irinel, Strouse, Geoffrey F., Yang, Wei, Florida State University, College of Arts and Sciences, Department of Chemistry & Biochemistry
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Abstract/Description: Spin-polarized unrestricted density functional theory is used to calculate the molecular properties of magnetic semiconductor quantum dots doped with 3d-metal atoms. We calculate total energies of the low spin antiferromagnetically coupled states using a spin-flipping algorithm leading to the broken-symmetry states. Given the novel nature of the materials studied, we simulate experimental observables such as hyperfine couplings, ionization/ energies, electron affinities, first and second...
Show moreSpin-polarized unrestricted density functional theory is used to calculate the molecular properties of magnetic semiconductor quantum dots doped with 3d-metal atoms. We calculate total energies of the low spin antiferromagnetically coupled states using a spin-flipping algorithm leading to the broken-symmetry states. Given the novel nature of the materials studied, we simulate experimental observables such as hyperfine couplings, ionization/ energies, electron affinities, first and second order polarizabilities, band gaps and exchange coupling constants. Specifically, we begin our investigation with pure clusters of (CdSe)_16 and demonstrate the dependence of molecular observables on geometrical structures. We also show that the many isomers of this cluster are energetically quite closely spaced, and thus it would be necessary to employ a battery of tests to experimentally distinguish them. Next, we discuss Mn-doping into the cage (CdSe)_9 cluster as well as the zinc-blende stacking type cluster (CdSe)_36. We show that the local exchange coupling mechanism is ligand-mediated superexchange and simulate the isotropic hyperfine constants. Finally, we discuss a novel study where (CdSe)_9 is doped with Mn or Fe up to a full replacement of all the Cd's and discuss the transition points for the magnetic behavior and specifically the greatly differing band-gap shifts. We also outline an unexpected pattern in the polarizability of the material as metals are added and compare our results with the results from theoretical studies of the bulk material.
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Date Issued: 2017
Identifier: FSU_2017SP_Gutsev_fsu_0071E_13781
Format: Thesis

Title: Quantum Oscillations in Two Dimensional Dirac and Weyl Semimetals.
Creator: Das, Suvadip, Manousakis, Efstratios, Bonesteel, N. E., Balicas, Luis, Piekarewicz, Jorge, Florida State University, College of Arts and Sciences, Department of Physics
Abstract/Description: Since the discovery of the exotic properties of graphene, two dimensional materials such as metal chalcogenides, transition metal oxides and other 2D compounds have gained renewed interest. Graphene, silicene, germanene, graphyne and boron allotropes form a rare class of 2D Dirac materials. The presence of such Dirac points near the Fermi level provides us the option to switch between two carrier types by slightly doping the material and could lead to potential optoelectronic devices....
Show moreSince the discovery of the exotic properties of graphene, two dimensional materials such as metal chalcogenides, transition metal oxides and other 2D compounds have gained renewed interest. Graphene, silicene, germanene, graphyne and boron allotropes form a rare class of 2D Dirac materials. The presence of such Dirac points near the Fermi level provides us the option to switch between two carrier types by slightly doping the material and could lead to potential optoelectronic devices. Recently discovered sister compounds WTe₂[2] and MoTe₂[62] have gained significant impetus for extremely pronounced nonsaturating magnetroresistance and topological semimetal hosting type II Weyl points. Further, a new class of two dimensional materials with multiple Dirac cones were discovered following the compound Zr₂Te₂P , and include the compounds Hf₂Te₂P , Zr₂Te₂As and Ti₂Te₂P. Quantum oscillation studies were performed to investigate the detailed Fermi surfaces and the topological properties such as Berry phase were obtained for the newly discovered two dimensional materials at the National High Magnetic Field Laboratory. In this thesis we will address the electronic structure, density of states and Fermi surface in all of these materials using Density Functional Theory and related methodology. The low energy (near Fermi energy) physics of all the materials studied are characterized by Dirac-like or Weyl- like electronic structure. Namely, the electrons obey Dirac-like or Weyl-like equations where the speed of light is replaced by the Fermi velocity. Furthermore, these materials share fundamental topological properties at the electronic low energy spectrum. Therefore, we wish to undertake the task of studying such fundamental properties from first principles.
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Date Issued: 2016
Identifier: FSU_FA2016_Das_fsu_0071E_13587
Format: Thesis

Title: Water and Air Flows in Karstic Caves and Conduits.
Creator: Khazmutdinova, Karina, Moore, Nicolas, Ye, Ming, Tam, Christopher K. W., Huettel, Markus, Florida State University, College of Arts and Sciences, Program in Geophysical Fluid...
Show moreKhazmutdinova, Karina, Moore, Nicolas, Ye, Ming, Tam, Christopher K. W., Huettel, Markus, Florida State University, College of Arts and Sciences, Program in Geophysical Fluid Dynamics
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Abstract/Description: This dissertation seeks to understand physical processes in submerged and dry caves in Florida. First, for submerged caves, we prove the possibility of an upward saline water intrusion due to the Venturi effect occurring in a submerged cave's restrictions, i.e. narrow connections between two otherwise large tunnels. A model is developed to obtain an analytical solution for estimating the saltwater discharge through caves into freshwater aquifers. Additionally, Florida springs are examined,...
Show moreThis dissertation seeks to understand physical processes in submerged and dry caves in Florida. First, for submerged caves, we prove the possibility of an upward saline water intrusion due to the Venturi effect occurring in a submerged cave's restrictions, i.e. narrow connections between two otherwise large tunnels. A model is developed to obtain an analytical solution for estimating the saltwater discharge through caves into freshwater aquifers. Additionally, Florida springs are examined, and the saltwater discharges due to the Venturi effect are calculated to be between 0.02 to 0.23 m3/s, which is significant especially for the springs with a mean annual freshwater discharge of less than 10 m3/s. Second, in an effort to develop a deeper understanding of dry caves, the microclimate of the so-called Dragon's Tooth Cave is examined. The ventilation patterns are analyzed by using in-situ measurements of temperature, CO2, and Radon-222. Estimated cave air renewal times vary from 2.4 days at the Entrance room to 6.6 days at the Dragon's Belly room. Next, a theoretical model is developed that uses outside temperatures to predict ventilation rates. Combined with simple first-order CO2 and Radon-222 mass balances, the model predicts net CO2 and Radon-222 concentrations in the cave, and shows an excellent agreement with the measurements.
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Date Issued: 2016
Identifier: FSU_FA2016_Khazmutdinova_fsu_0071E_13545
Format: Thesis

Title: Experimental and Computational Studies on DNA Electrophoresis in Lyotropic Polymer Liquid Crystals.
Creator: Wei, Ling, Van Winkle, David H., Shanbhag, Sachin, Xiong, Peng, Rikvold, Per Arne, Wahl, Horst D., Florida State University, College of Arts and Sciences, Department of Physics
Abstract/Description: Electrophoresis as an analytical technique has made considerable contributions to the separations and analysis of macromolecules in biology-related research. Pluronic gels, which are composed of orderly packed spherical micelles assembled by tri-block copolymers, have been developed as novel sieving media to separate oligonucleotides, duplex DNA molecules and proteins, providing ease of manipulations due to their thermo-reversibility and higher resolution in comparison with other polymer gels...
Show moreElectrophoresis as an analytical technique has made considerable contributions to the separations and analysis of macromolecules in biology-related research. Pluronic gels, which are composed of orderly packed spherical micelles assembled by tri-block copolymers, have been developed as novel sieving media to separate oligonucleotides, duplex DNA molecules and proteins, providing ease of manipulations due to their thermo-reversibility and higher resolution in comparison with other polymer gels. Electrophoretic mobility of short double-stranded DNA molecules in pluronic F127 is reported to have a non-monotonic dependence on DNA length, which is not observed in other polymer-based sieving media or explained by any well-developed theories. In this dissertation, the unusual DNA-length dependence of electrophoretic mobility is experimentally investigated in several different pluronic gels, and the DNA dynamics in pluronic liquid crystals is systematically studied by coarse-grained Brownian dynamics simulations. The crystal structures and micelle dimensions of pluronics P105, P123 and F127 are characterized by atomic force microscopy, small-angle x-ray scattering, small-angle neutron scattering and dynamic light scattering. Two-dimensional gel electrophoresis is performed and the electrophoretic mobility of DNA molecules in the size range of 20-500 bp is measured in pluronics P105, P123 and F127. The unusual DNA length-dependent mobility is consistently obtained in three pluronic gels, where the mobility of very short DNA molecules increases with increasing DNA length, and the mobility of long DNA molecules monotonically decreases with DNA length. Superposed on the rising and falling trends are the subtle oscillations of mobility with DNA length in the intermediate regime. Brownian dynamics simulations are implemented to numerically calculate the DNA mobility in pluronic lattices, by including the short-ranged intra-molecular hydrodynamic interactions, and modeling the interactions between DNA molecules and pluronic micelles via a repulsive force and entanglement effect. The rise, fall and oscillations of mobility with DNA length, as obtained in experimental measurements, are reproduced by the Brownian dynamics simulations, and essential physics that dominates the unusual features of mobility is extracted from the simulations. In addition, electric field-dependent mobility of DNA molecules in pluronic lattices is studied by Brownian dynamics simulations, and the conceptual connection between high-field simulations along specific field directions and low-field experiments in bulk gels is established, and the Brownian dynamic simulations are proven to be an appropriate approach to interpret the DNA electrophoretic dynamics in pluronic matrices. Moreover, electrophoretic mobility of duplex DNA flanked by single-stranded overhangs is measured in pluronic gels, and it is shown that the mobility of DNA with overhangs is higher than the corresponding blunt-ended DNA molecules. Brownian dynamics simulations are carried out, and the enhancement of mobility for DNA with overhangs is captured by the simulations. By integrating numerical simulations with experimental measurements, the fundamental physical quantities and interactions that manipulate the DNA electrophoretic migration in pluronic liquid crystals are revealed. Understanding the unusual DNA length-dependent mobility in pluronic gels potentially provides profound insights in designing and optimizing high-performance sieving matrices for size-based separation purposes.
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Date Issued: 2016
Identifier: FSU_FA2016_Wei_fsu_0071E_13585
Format: Thesis

Title: Development and Characterization of a Novel Continuously Flowing Liquid Film Plasma Reactor for Chemical Synthesis.
Creator: Wandell, Robert J. (Robert Jay), Locke, Bruce R., Alabugin, Igor V., Chella, Ravindran, Hallinan, Daniel T., Florida State University, College of Engineering, Department of...
Show moreWandell, Robert J. (Robert Jay), Locke, Bruce R., Alabugin, Igor V., Chella, Ravindran, Hallinan, Daniel T., Florida State University, College of Engineering, Department of Chemical and Biomedical Engineering
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Abstract/Description: The aim of this work is to develop a deeper understanding of the nuances involved in designing and optimizing the performance of gas/liquid plasma reactors for chemical synthesis. The design of such reactors requires integrating knowledge from a number of scientific disciplines including mechanical engineering (reactor construction), electrical engineering (power network design and electrical diagnostics), physics (plasma formation and diagnostics), chemical engineering, (reactor design,...
Show moreThe aim of this work is to develop a deeper understanding of the nuances involved in designing and optimizing the performance of gas/liquid plasma reactors for chemical synthesis. The design of such reactors requires integrating knowledge from a number of scientific disciplines including mechanical engineering (reactor construction), electrical engineering (power network design and electrical diagnostics), physics (plasma formation and diagnostics), chemical engineering, (reactor design, transport phenomena / modeling), and chemistry (chemical analysis). Due to the complicated nature of such a multidisciplinary study, complete analysis of a single reactor system is difficult and rarely performed with accuracy, especially for a variety of operating conditions. In this work, a novel continuously flowing liquid film plasma reactor was developed and fully characterized under the above criteria for a range of operating conditions in order to better understand which variables most significantly impact the generation of hydrogen peroxide from pure water and argon gas. This work shows that increases in the energy yield for hydrogen peroxide with pulsed plasma discharge is possible by variation of the plasma properties to reduce the amount of "wasted" energy which does not contribute to desired chemical reactions. In addition, increases in the production rate of hydrogen peroxide without a loss in energy yield is shown to be possible by increasing the pulse frequency while simultaneously decreasing the gas phase residence time. The high concentration of hydroxyl radicals produced by this system was also used to partially oxidize simple organic compounds into higher value products.
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Date Issued: 2016
Identifier: FSU_FA2016_Wandell_fsu_0071E_13556
Format: Thesis

Title: Modeling and Simulating Vortex Pinning and Transport Currents for High Temperature Superconductors.
Creator: Sockwell, K. Chadwick (Kenneth Chadwick), Gunzburger, Max D., Peterson, Janet S., Burkardt, John V., Florida State University, College of Arts and Sciences, Department of...
Show moreSockwell, K. Chadwick (Kenneth Chadwick), Gunzburger, Max D., Peterson, Janet S., Burkardt, John V., Florida State University, College of Arts and Sciences, Department of Scientific Computing
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Abstract/Description: Superconductivity is a phenomenon characterized by two hallmark properties, zero electrical resistance and the Meissner effect. These properties give great promise to a new generation of resistance free electronics and powerful superconducting magnets. However this possibility is limited by the extremely low critical temperature the superconductors must operate under, typically close to 0K. The recent discovery of high temperature superconductors has brought the critical temperature closer to...
Show moreSuperconductivity is a phenomenon characterized by two hallmark properties, zero electrical resistance and the Meissner effect. These properties give great promise to a new generation of resistance free electronics and powerful superconducting magnets. However this possibility is limited by the extremely low critical temperature the superconductors must operate under, typically close to 0K. The recent discovery of high temperature superconductors has brought the critical temperature closer to room temperature than ever before, making the realization of room temperature superconductivity a possibility. Simulations of superconducting technology and materials will be necessary to usher in the new wave of superconducting electronics. Unfortunately these new materials come with new properties such as effects from multiple electron bands, as is the case for magnesium diboride. Moreover, we must consider that all high temperature superconductors are of a Type II variety, which possess magnetic tubes of flux, known as vortices. These vortices interact with transport currents, creating an electrical resistance through a process known as flux flow. Thankfully this process can be prevented by placing impurities in the superconductor, pinning the vortices, making vortex pinning a necessary aspect of our model. At this time there are no other models or simulations that are aimed at modeling vortex pinning, using impurities, in two-band materials. In this work we modify an existing Ginzburg-Landau model for two-band superconductors and add the ability to model normal inclusions (impurities) with a new approach which is unique to the two-band model. Simulations in an attempt to model the material magnesium diboride are also presented. In particular simulations of vortex pinning and transport currents are shown using the modified model. The qualitative properties of magnesium diboride are used to validate the model and its simulations. One main goal from the computational end of the simulations is to enlarge the domain size to produce more realistic simulations that avoid boundary pinning effects. In this work we also implement the numerical software library Trilinos in order to parallelize the simulation to enlarge the domain size. Decoupling methods are also investigated with a goal of enlarging the domain size as well. The One-Band Ginzburg-Landau model serves as a prototypical problem in this endeavor and the methods shown that enlarge the domain size can be easily implemented in the two-band model.
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Date Issued: 2016
Identifier: FSU_FA2016_Sockwell_fsu_0071N_13577
Format: Thesis

Title: Computational Studies of Equilibrium and Non-Equilibrium Phase Diagrams and Critical Properties of Two Physical and Chemical Model Systems with Both Short-Range and Long-Range Interactions or Reactivities.
Creator: Chan, Chor-Hoi, Rikvold, Per Arne, Shanbhag, Sachin, Brown, Gregory, Capstick, Simon, Xiong, Peng, Florida State University, College of Arts and Sciences, Department of Physics
Abstract/Description: In this dissertation, we introduce long-range interactions into one equilibrium model (Ising model) and one non-equilibrium system (Ziff-Gulari-Barshad model), and study their phase diagrams and critical properties. A new approach to do Wang-Landau simulation: macroscopically constrained Wang-Landau, is proposed in connection with the former system. Our macroscopically constrained Wang-Landau method breaks a multidimensional random walk process in phase space into many separate, one...
Show moreIn this dissertation, we introduce long-range interactions into one equilibrium model (Ising model) and one non-equilibrium system (Ziff-Gulari-Barshad model), and study their phase diagrams and critical properties. A new approach to do Wang-Landau simulation: macroscopically constrained Wang-Landau, is proposed in connection with the former system. Our macroscopically constrained Wang-Landau method breaks a multidimensional random walk process in phase space into many separate, one-dimensional random walk processes in the energy space. Each of these random walks is constrained to a different value of the macroscopic order parameters. By knowing the distribution of these constrained variables, we can deduce the multi-variable density of states. When the multi-variable density of states for one set of external parameters is obtained, the density of states at any point in the phase diagram can be obtained by simple transformations. After that, all thermodynamic quantities can be obtained. We apply this method to an antiferromagnetic Ising model with a ferromagnetic long-range interaction. The addition of the long-range interaction induces metastable regions in the phase diagram, and a mean-field class critical point emerges for sufficiently strong long-range interaction. We demonstrate how to use the multi-variable density of states obtained to sketch out the complicated phase diagrams for different values of the long-range interaction. We also give free-energy plots, and plots of the distributions of the order parameters of the system for different special points in these phase diagrams. The Ziff-Gulari-Barshad (ZGB) model, a simplified description of the oxidation of carbon monoxide (CO) on a catalyst surface, is widely used to study properties of nonequilibrium phase transitions. Instead of restricting the CO and atomic oxygen (O) to react to form carbon dioxide (CO₂) only when they are adsorbed in close proximity, we consider a modified model that includes an adjustable probability for adsorbed CO and O atoms located far apart on the lattice to react. We employ large-scale Monte Carlo simulations to study the critical properties of this system. We find that the nonequilibrium critical point changes from the two-dimensional Ising universality class to the mean-field universality class upon introducing even a weak long-range reactivity mechanism.
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Date Issued: 2016
Identifier: FSU_FA2016_Chan_fsu_0071E_13552
Format: Thesis

Title: A Dalitz Plot Analysis and Extraction of Spin Density Matrix Elements for the Ω → 3Π Decay.
Creator: Zeoli, Christopher Paul, Crede, Volker, Sura, Philip, Eugenio, Paul Michael, Roberts, Winston, Adams, Todd, Florida State University, College of Arts and Sciences, Department of...
Show moreZeoli, Christopher Paul, Crede, Volker, Sura, Philip, Eugenio, Paul Michael, Roberts, Winston, Adams, Todd, Florida State University, College of Arts and Sciences, Department of Physics
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Abstract/Description: At the Continuous Electron Beam Accelerator Facility (CEBAF) at Jefferson National Laboratory (JLab), $\omega$ vector-mesons were photo-produced off a fixed, liquid-hydrogen target during the 2009 run-period via the reaction $\gamma p \rightarrow p \omega$. The charged final-state particles from the $\omega$~resonance decays were detected by the CEBAF Large Acceptance Spectrometer (CLAS). With a combination of measurements which involved the use of time and energy-deposit counters as well as...
Show moreAt the Continuous Electron Beam Accelerator Facility (CEBAF) at Jefferson National Laboratory (JLab), $\omega$ vector-mesons were photo-produced off a fixed, liquid-hydrogen target during the 2009 run-period via the reaction $\gamma p \rightarrow p \omega$. The charged final-state particles from the $\omega$~resonance decays were detected by the CEBAF Large Acceptance Spectrometer (CLAS). With a combination of measurements which involved the use of time and energy-deposit counters as well as reconstructed drift chamber (DC) tracks, the 4-momenta and vertices of the initial- and charged final-state particles were determined. Subsequent to reconstruction, event selection, kinematic fitting, signal and background separation, and detector efficiency simulation of the data for the three-pion final-state, i.e. $\omega \rightarrow \pi^+~\pi^-~(\pi^0)$, the Florida State University (FSU) Experimental Hadronic Nuclear Group has extracted the differential production cross section.\\ \indent With such data and the measured differential cross section in hand, I have conducted a Dalitz plot analysis of the $\omega \rightarrow 3\pi$ decay in close cooperation with the Joint Physics Analysis Center (JPAC) at JLab. The decay probability density separates into angle-dependent and -independent factors: the Spin Density Distribution (SDD) which is proportional to the differential cross section, and the reduced decay distribution (RDD) which is proportional to the decay width, respectively. The Spin Density Matrix Elements (SDMEs) for an unpolarized beam were obtained from fitting the SDD. In addition, fits for two different RDDs, i.e. a Dalitz plot distribution and a JPAC distribution, have been underway. The former is a truncated polynomial expansion of Lorentz Invariant Dalitz plot variables. The latter was based on the isobar model of the $\omega$ decay. Having made use of sub-energy unitarity, this model accounts for both elastic and inelastic 3-body re-scattering effects. Plus, fitting this model to measured data is a first. A comparison through fit parameters of each reduced distribution is intended. Lastly, my results and as well as a discussion of future extensions to this study and the prospects for similar light-meson-decay analyses are concluded at the end of this thesis.\\
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Date Issued: 2016
Identifier: FSU_FA2016_Zeoli_fsu_0071E_13456
Format: Thesis

Title: Measurement of Polarization Observables in Vector Meson Photoproduction Using a Transversely-Polarized Frozen-Spin Target and Polarized Photons at CLAS, Jefferson Lab.
Creator: Roy, Priyashree, Crede, Volker, Plewa, Tomasz, Capstick, Simon, Eugenio, Paul Michael, Prosper, Harrison B., Florida State University, College of Arts and Sciences, Department...
Show moreRoy, Priyashree, Crede, Volker, Plewa, Tomasz, Capstick, Simon, Eugenio, Paul Michael, Prosper, Harrison B., Florida State University, College of Arts and Sciences, Department of Physics
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Abstract/Description: The study of baryon resonances provides a deeper understanding of the strong interaction because the dynamics and relevant degrees of freedom hidden within them are reflected by the properties of the excited states of baryons. Higher-lying excited states at and above 1.7 GeV/c² are generally predicted to have strong couplings to final states involving a heavier meson, e. g. one of the vector mesons, ρ, ω, φ, as compared to a lighter pseudoscalar meson, e.g. π and η. Decays to the ππN final...
Show moreThe study of baryon resonances provides a deeper understanding of the strong interaction because the dynamics and relevant degrees of freedom hidden within them are reflected by the properties of the excited states of baryons. Higher-lying excited states at and above 1.7 GeV/c² are generally predicted to have strong couplings to final states involving a heavier meson, e. g. one of the vector mesons, ρ, ω, φ, as compared to a lighter pseudoscalar meson, e.g. π and η. Decays to the ππN final states via π∆ also become more important through the population of intermediate resonances. We observe that nature invests in mass rather than momentum. The excited states of the nucleon are usually found as broadly overlapping resonances which may decay into a multitude of final states involving mesons and baryons. Polarization observables make it possible to isolate single-resonance contributions from other interference terms. The CLAS g9 (FROST) experiment, as part of the N∗ spectroscopy program at Jefferson Laboratory, accumulated photoproduction data using circularly- and linearly-polarized photons incident on a transversely-polarized butanol target (g9b experiment) in the photon energy range 0.3 − 2.4 GeV & 0.7 − 2.1 GeV, respectively. In this work, the analysis of reactions and polarization observables which involve two charged pions, either in the fully exclusive reaction γp → pπ⁺π⁻ or in the semi-exclusive reaction with a missing neutral pion, γp → pπ⁺π⁻ (π⁰) will be presented. For the reaction γp → pπ⁺π⁻ , eight polarization observables (I[superscript s], I[superscript c], P[subscript x], P[subscript y], P[superscript s][subscript x,y], P[superscript c][subscript x,y]) have been extracted. The high statistics data rendered it possible to extract these observables in three dimensions. All of them are first-time measurements. The fairly good agreement of I[superscript s] and I[superscript c] obtained from this analysis with the experimental results from a previous CLAS experiment provides support for the first time measurements. For the reaction γp → pω → pπ⁺ π⁻ (π⁰), five polarization observables (T , Σ, F , H, P ) have been extracted, four of which are first-time measurements at all energies. This analysis thus represents a comprehensive program on vector-meson photoproduction: The ω is observed and studied directly from the data and the polarization observables for the (broad) ρ can be extracted from the double-pion reaction in a partial-wave analysis. The 13 polarization observables extracted in this analysis substantially augment the world database of polarization observables for these reactions and are expected to play a crucial role in identifying the contributing baryon resonances.
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Date Issued: 2016
Identifier: FSU_FA2016_Roy_fsu_0071E_13542
Format: Thesis

Title: Magnetothermal Transport and Elastoresistive Properties of Low-Dimensional Magnetoelectrics and Dichalcogenides.
Creator: Benjamin, Shermane Mark, Choi, Eun Sang, Manousakis, Efstratios, Oates, William, Reina, Laura, Beekman, Christianne, Florida State University, College of Arts and Sciences,...
Show moreBenjamin, Shermane Mark, Choi, Eun Sang, Manousakis, Efstratios, Oates, William, Reina, Laura, Beekman, Christianne, Florida State University, College of Arts and Sciences, Department of Physics
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Abstract/Description: Co₄Nb₂O₉ is a quasi two dimensional material that has been known to exhibit magnetoelectric behavior with an antiferromagnetic transition (T[subscript N]) at ∼ 27 K. Our findings reveal strong evidence of magnon heat transport below T[subscript N] through magnetothermal conductivity measurements. Magnetothermal coupling is strongest below 2 K around 0.2 T suggesting presence of the thermal heat-valve effect causing an increase in its thermal conductivity by nearly 4-fold. Independent of field...
Show moreCo₄Nb₂O₉ is a quasi two dimensional material that has been known to exhibit magnetoelectric behavior with an antiferromagnetic transition (T[subscript N]) at ∼ 27 K. Our findings reveal strong evidence of magnon heat transport below T[subscript N] through magnetothermal conductivity measurements. Magnetothermal coupling is strongest below 2 K around 0.2 T suggesting presence of the thermal heat-valve effect causing an increase in its thermal conductivity by nearly 4-fold. Independent of field, we not only see the presence of phonon-magnon resonant scattering but also strong phonon-spin coupling; giving rise to an anisotropic thermal conductivity where within the plane of spins conductivity is greater than inter-plane. Thermal measurements were also carried out on Ba₃Cr₂O₈ which has been shown to undergo Bose-Einstein condensation of magnetic excitations. Through intercalation with copper and palladium atoms between the layers of the transition metal dichalcogenides titanium diselenide (TiSe₂), it has previously been shown that where the intrinsic charge density wave’s (CDW) temperature dependent resistivity peak anomaly occurs (T[subscript cdw] ∼165 K) decreases with increased intercalation and/or hydrostatic pressure. To mimic the chemical pressure caused by intercalation, uniaxial physical pressure (both compression and expansion) is used along with the Poisson effect. In the experiment with compressive pressure perpendicular to the layers (c-axis), resistivity data shows a shift in the peak (T[subscript cdw]) towards lower temperatures; expected for increasing dimensionality. For uniaxial pressure parallel to the layers, the Poisson effect should separate the layers, providing a separation of the layers similar to that of intercalation. Preliminary results show T[subscript cdw] increases initially, and then decreases. A prototype to induce uniaxial tension perpendicular to the layers has recently been developed and preliminary results will be reported. Electrical transport measurements were also executed for the first time on the first FE(II)-TCNQ spin cross-over (SCO) system ever synthesized. In fact, our material is the first structurally defined magnetically bistable semiconductor to be constructed from TCNQ radical ions. With the aid of spider silk fibers (detailed in further sections), our findings show it is a narrow band-gap semiconductor where its activation energy changes from 110 meV to 10 meV as it crosses the SCO transition temperature to lower temperature.
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Date Issued: 2016
Identifier: FSU_FA2016_Benjamin_fsu_0071E_13618
Format: Thesis

Title: Entangling Qubits by Heisenberg Spin Exchange and Anyon Braiding.
Creator: Zeuch, Daniel, Bonesteel, N. E., Sussman, Mark, Hill, S. (Stephen Olof), Piekarewicz, Jorge, Florida State University, College of Arts and Sciences, Department of Physics
Abstract/Description: As the discovery of quantum mechanics signified a revolution in the world of physics more than one century ago, the notion of a quantum computer in 1981 marked the beginning of a drastic change of our understanding of information and computability. In a quantum computer, information is stored using quantum bits, or qubits, which are described by a quantum-mechanical superposition of the quantum states 0 and 1. Computation then proceeds by acting with unitary operations on these qubits. These...
Show moreAs the discovery of quantum mechanics signified a revolution in the world of physics more than one century ago, the notion of a quantum computer in 1981 marked the beginning of a drastic change of our understanding of information and computability. In a quantum computer, information is stored using quantum bits, or qubits, which are described by a quantum-mechanical superposition of the quantum states 0 and 1. Computation then proceeds by acting with unitary operations on these qubits. These operations are referred to as quantum logic gates, in analogy to classical computation where bits are acted on by classical logic gates. In order to perform universal quantum computation it is, in principle, sufficient to carry out single-qubit gates and two-qubit gates, where the former act on individual qubits and the latter, acting on two qubits, are used to entangle qubits with each other. The present thesis is divided into two main parts. In the first, we are concerned with spin-based quantum computation. In a spin-based quantum computer, qubits are encoded into the Hilbert space spanned by spin-½ particles, such as electron spins trapped in semiconductor quantum dots. For a suitable qubit encoding, turning on-and-off, or "pulsing," the isotropic Heisenberg exchange Hamiltonian JSi · Sj allows for universal quantum computation and it is this scheme, known as exchange-only quantum computation, which we focus on. In the second part of this thesis, we consider a topological quantum computer in which qubits are encoded using so-called Fibonacci anyons, exotic quasiparticle excitations that obey non-Abelian statistics, and which may emerge in certain two-dimensional topological systems such as fractional quantum-Hall states. Quantum gates can then be carried out by moving these particles around one another, a process that can be viewed as braiding their 2+1 dimensional worldlines. The subject of the present thesis is the development and theoretical understanding of procedures used for entangling qubits. We begin by presenting analytical constructions of pulse sequences which can be used to carry out two-qubit gates that are locally equivalent to a controlled-PHASE gate. The corresponding phase can be arbitrarily chosen, and for one particular choice this gate is equivalent to controlled-NOT. While the constructions of these sequences are relatively lengthy and cumbersome, we further provide a straightforward and intuitive derivation of the shortest known two-qubit pulse sequence for carrying out a controlled-NOT gate. This derivation is carried out completely analytically through a novel "elevation" of a simple three-spin pulse sequence to a more complicated five-spin pulse sequence. In the case of topological quantum computation with Fibonacci anyons, we present a new method for constructing entangling two-qubit braids. Our construction is based on an iterative procedure, established by Reichardt, which can be used to systematically generate braids whose corresponding operations quickly converge towards an operation that has a diagonal matrix representation in a particular natural basis. After describing this iteration procedure we show how the resulting braids can be used in two explicit constructions for two-qubit braids. Compared to two-qubit braids that can be found using other methods, the braids generated here are among the most efficient and can be obtained straightforwardly without computational overhead.
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Date Issued: 2016
Identifier: FSU_2016SU_Zeuch_fsu_0071E_13323
Format: Thesis

Title: Novel Pd and Chalcogen Based Low-Dimensional Superconductors and Electronic Properties of Type-I Weyl Semimetals.
Creator: Zhang, Qiu Run, Balicas, Luis, Schlottmann, P., Siegrist, Theo M., Chiorescu, Irinel, Riley, Mark A., Florida State University, College of Arts and Sciences, Department of Physics
Abstract/Description: This thesis investigates a new family of Pd based transition metal chalcogenides which displays unconventional superconducting behavior and also the newly discovered Weyl physics in transition metal monopnictides. The superconductors investigated are Nb₂Pd₀.₈₁S₅ (NPS215), Nb₃PdxSe₇ (NPSe317), Ta₄Pd₃Te₁₆ (TPT) and chemically substituted compounds. The Nb based samples displayed relatively low superconducting transition temperatures, but extremely high upper critical fields Hbc2 that exceeded...
Show moreThis thesis investigates a new family of Pd based transition metal chalcogenides which displays unconventional superconducting behavior and also the newly discovered Weyl physics in transition metal monopnictides. The superconductors investigated are Nb₂Pd₀.₈₁S₅ (NPS215), Nb₃PdxSe₇ (NPSe317), Ta₄Pd₃Te₁₆ (TPT) and chemically substituted compounds. The Nb based samples displayed relatively low superconducting transition temperatures, but extremely high upper critical fields Hbc2 that exceeded the weak coupling Pauli limiting fields by a factor considerably greater than two. For a NPS215 crystal with Tc ∼ 6.7 K, Hbc2 (T ➝ 0K) = 37 T. For NPSe317, we found crystals with Tc = 1.87 K and 3.5 K, Hbc2 (T ➝ 0K) = 14.1 T and 28 T. Both compounds also displayed unconventional behavior, in the case of NPS215, Hc₂'s do not saturate even for temperatures down to T = 0.4 K and H⊥bc2 remained linear in the whole temperature range. For NPSe317, H⊥bc2s are well described by the Ginzburg-Landau expression where they saturated at the lowest temperatures. H‖bc2 in the samples with Tc ≅ 3.5 K showed a -T½ dependence, such behavior was only observed in the two-dimensional superconductivity of atomically thin NbSe₂. The high superconducting anisotropy together with Fermi surface calculations indicate that these systems are low dimensional superconducting systems. The TPT samples showed linear in T non-saturating Hc₂s for all three orientations, but their magnitudes are comparatively small and the system seems to be orbital limited. Quantum oscillations revealed that the Weyl semimetals, (Nb,Ta)(P,As), have small Fermi surfaces with a non-trivial Berry phase. The chiral anomaly was observed in the form of negative magnetoresistivity when H‖j. The SdH and dHvA oscillations observed at low magnetic fields experience changes in amplitude and in periodicity upon reaching the quantum limit of the systems. Coupled with field induced effective mass renormalization points towards electronic/topological phase transition(s) in these semimetals. Anomalous Hall effect was observed in these systems and there appears to be nearly quantized Hall plateaus that are nearly linearly quantized..
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Date Issued: 2016
Identifier: FSU_2016SU_Zhang_fsu_0071E_13363
Format: Thesis

Title: Targeting the Minimal Supersymmetric Standard Model with the Compact Muon Solenoid Experiment.
Creator: Bein, Samuel Louis, Prosper, Harrison B., Ruse, Michael, Askew, Andrew, Okui, Takemichi, Piekarewicz, Jorge, Florida State University, College of Arts and Sciences, Department...
Show moreBein, Samuel Louis, Prosper, Harrison B., Ruse, Michael, Askew, Andrew, Okui, Takemichi, Piekarewicz, Jorge, Florida State University, College of Arts and Sciences, Department of Physics
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Abstract/Description: An interpretation of CMS searches for evidence of supersymmetry in the context of the minimal supersymmetric Standard Model (MSSM) is given. It is found that supersymmetric particles with color charge are excluded in the mass range below about 400 GeV, but neutral and weakly-charged sparticles remain non-excluded in all mass ranges. Discussion of the non-excluded regions of the model parameter space is given, including details on the strengths and weaknesses of existing searches, and...
Show moreAn interpretation of CMS searches for evidence of supersymmetry in the context of the minimal supersymmetric Standard Model (MSSM) is given. It is found that supersymmetric particles with color charge are excluded in the mass range below about 400 GeV, but neutral and weakly-charged sparticles remain non-excluded in all mass ranges. Discussion of the non-excluded regions of the model parameter space is given, including details on the strengths and weaknesses of existing searches, and recommendations for future analysis strategies. Advancements in the modeling of events arising from quantum chromodynamics and electroweak boson production, which are major backgrounds in searches for new physics at the LHC, are also presented. These methods have been implemented as components of CMS searches for supersymmetry in proton-proton collisions resulting in purely hadronic events (i.e., events with no identified leptons) at a center of momentum energy of 13 TeV. These searches, interpreted in the context of simplified models, exclude supersymmetric gluons (gluinos) up to masses of 1400 to 1600 GeV, depending on the model considered, and exclude scalar top quarks with masses up to about 800 GeV, assuming a massless lightest supersymmetric particle. A search for non-excluded supersymmetry models is also presented, which uses multivariate discriminants to isolate potential signal candidate events. The search achieves sensitivity to new physics models in background-dominated kinematic regions not typically considered by analyses, and rules out supersymmetry models that survived 7 and 8 TeV searches performed by CMS.
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Date Issued: 2016
Identifier: FSU_2016SU_Bein_fsu_0071E_13432
Format: Thesis

Title: Optical Spectroscopy of Novel Semiconductors in High Magnetic Fields.
Creator: Ludwig, Jonathan, Smirnov, Dmitry, Cao, Jianming, Knappenberger, Kenneth L., Schlottmann, P., Tabor, Samuel Lynn, Florida State University, College of Arts and Sciences,...
Show moreLudwig, Jonathan, Smirnov, Dmitry, Cao, Jianming, Knappenberger, Kenneth L., Schlottmann, P., Tabor, Samuel Lynn, Florida State University, College of Arts and Sciences, Department of Physics
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Abstract/Description: Understanding new quantum phenomena and properties of new materials is the foundation of condensed matter physics. One can mention celebrated examples of integer and fractional quantum Hall effect, Aharonov-Bohm quantum interference effects, inventions of heterostructures and superlattices, and a recent discover of Dirac-like quasiparticles in atomically thin 2D crystals. Here we employ optical spectroscopy combined with large magnetic field and low temperatures to probe the electronic...
Show moreUnderstanding new quantum phenomena and properties of new materials is the foundation of condensed matter physics. One can mention celebrated examples of integer and fractional quantum Hall effect, Aharonov-Bohm quantum interference effects, inventions of heterostructures and superlattices, and a recent discover of Dirac-like quasiparticles in atomically thin 2D crystals. Here we employ optical spectroscopy combined with large magnetic field and low temperatures to probe the electronic structure of several novel semiconductor materials. The discovery of graphene has opened the door to the study of other 2D materials. Here we focus on a new family of semiconducting layered 2D materials known as transition metal dichalcogenides (TMDs), which have recently emerged as a new class of direct bandgap 2D semiconductors with two degenerate, but non-equality valleys at the ±K points in the Brillouin zone. Due to the broken inversion symmetry in monolayer TMDs, this valley degree of freedom can be selectively addressed by optical helicity, opening the possibility for valleytronic and optoelectronic applications. By performing valley selective photoluminescence measurements on TMDs we demonstrate the lifting of the valley degeneracy and valley polarization in an applied perpendicular magnetic field. One of the most remarkable properties of graphene is its linear dispersion. Once relegated only to the realm of theoretical exploration, the past ten years has seen an explosion in the realization of new Dirac-like materials in condensed matter systems. One of the most important of these new Dirac-like materials is HgTe quantum wells (QWs). Here, we report on Landau level spectroscopy studies of a series of HgTe QWs grown near or at the critical well thickness, where the band gap vanishes. We observe a square root B dependence for the energy of the dominant cyclotron resonance (CR) transition over the broad range of magnetic fields, characteristic of Dirac fermions. While not in the same family of Dirac-like or 2D materials, metamorphic InAs₁₋xSbx alloys are a promising narrow gap semiconductors with bandgaps as low as 0.1 eV. New growth techniques now allow for the realization of bulk unstrained, unrelaxed InAs₁₋xSbx layers. Here, we report on the systematic study of the electronic properties of a series of InAs₁₋xSbx alloys over a broad range of Sb concentrations by infrared magneto-absorption and magneto-transport.
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Date Issued: 2016
Identifier: FSU_2016SU_Ludwig_fsu_0071E_13434
Format: Thesis

Title: A Gamma-Ray Spectroscopy Study for Higher Spin Structure of ³¹Si.
Creator: Tai, Pei-Luan, Tabor, Samuel Lynn, Humayun, Munir, Riley, Mark A., Volya, Alexander, Reina, Laura, Florida State University, College of Arts and Sciences, Department of Physics
Abstract/Description: This work presents a comprehensive gamma-ray spectroscopic study to the higher spin structure of ³¹Si, including its excitation energies, spins, and branching ratios, along with the shell model discussions. ³¹Si was produced through the ¹⁸O(¹⁸O, alpha n) reaction at the beam energy of 25 MeV, which preferentially populates the higher spin states. The alpha particles from the reaction were detected in the Microball detector and the multiple gamma-ray coincidences were detected by GAMMASPHERE....
Show moreThis work presents a comprehensive gamma-ray spectroscopic study to the higher spin structure of ³¹Si, including its excitation energies, spins, and branching ratios, along with the shell model discussions. ³¹Si was produced through the ¹⁸O(¹⁸O, alpha n) reaction at the beam energy of 25 MeV, which preferentially populates the higher spin states. The alpha particles from the reaction were detected in the Microball detector and the multiple gamma-ray coincidences were detected by GAMMASPHERE. The ³¹Si recoil energies and angles were event-by-event kinematically reconstructed by using the information of the energies and angles of the alpha evaporations detected by Microball. The kinematic correction led to a better Doppler correction and allowed us to discover 26 new states and 49 newly-observed gamma transitions in total. 15 gamma-decaying states above the neutron separation energy were identified, and two highest gamma-decaying states are at the energies 9323- and 9216-keV. Spin and parity assignments are based on gamma-ray angular distribution analysis, DCO ratios analysis, branching ratio, and shell model predictions. For the positive-parity states predicted by the shell model calculations using USDA and WBP-a interactions agree well with the measured ones. But for the cross-shell states, the shell model calculations have RMS around 400-500 keV based on testing the lowest three measured negative parity states.
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Date Issued: 2016
Identifier: FSU_2016SU_Tai_fsu_0071E_13321
Format: Thesis

Title: A Search for Supersymmetry with Two Photons and Missing Transverse Energy at CMS at a Center of Mass Energy of 13 TeV.
Creator: Santra, Arka, Askew, Andrew, Tyson, Gary Scott, Adams, Todd, Reina, Laura, Piekarewicz, Jorge, Florida State University, College of Arts and Sciences, Department of Physics
Abstract/Description: The present theoretical framework to describe the universe in particle level, the Standard Model describes only 4% of the matter-energy budget of the universe. There are many theories which attempt to describe the universe beyond the scope of the Standard Model. This dissertation describes a search for supersymmetry, a beyond Standard Model theory, using data collected by the Compact Muon Solenoid detector with integrated luminosity of 2.3 fb⁻¹ at a center of mass energy of 13 TeV during 2015...
Show moreThe present theoretical framework to describe the universe in particle level, the Standard Model describes only 4% of the matter-energy budget of the universe. There are many theories which attempt to describe the universe beyond the scope of the Standard Model. This dissertation describes a search for supersymmetry, a beyond Standard Model theory, using data collected by the Compact Muon Solenoid detector with integrated luminosity of 2.3 fb⁻¹ at a center of mass energy of 13 TeV during 2015. The data were produced in proton-proton collisions at the Large Hadron Collider near Geneva, Switzerland. This search was performed with events having two photons and missing transverse energy in the final state. This final state was motivated by general gauge mediated supersymmetry breaking, one of the theories on how breaking of supersymmetry can be mediated. No significant excess over the expected background was observed. The result was interpreted with simplified model scans and 95% upper limit on production cross sections are provided.
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Date Issued: 2016
Identifier: FSU_2016SU_Santra_fsu_0071E_13394
Format: Thesis

Title: Alkaline Earth Metal Fluxes for the Growth of Single Crystal Oxides.
Creator: Ramirez, Daniel, Siegrist, Theo M., Hellstrom, Eric, Liang, Zhiyong Richard, Florida State University, Graduate School, Program in Materials Science
Abstract/Description: Oxide ceramics are materials with a wide range of properties. Insulators are most common, however semiconductors, strongly correlated electron materials, and even superconductors are all relevant oxide materials. Here we seek to synthesize novel oxide single crystal phases and study their properties using an alkaline earth metal flux technique. The specific flux techniques are new, and we will seek to understand the capabilities of these fluxes as a novel synthesis tool. The use of a barium...
Show moreOxide ceramics are materials with a wide range of properties. Insulators are most common, however semiconductors, strongly correlated electron materials, and even superconductors are all relevant oxide materials. Here we seek to synthesize novel oxide single crystal phases and study their properties using an alkaline earth metal flux technique. The specific flux techniques are new, and we will seek to understand the capabilities of these fluxes as a novel synthesis tool. The use of a barium metal flux to grow single crystal oxides is rather counterintuitive, but is exemplified further with the growth of europium monoxide (Fm3 #225, Z = 4). Eu₁₋xBaxO single crystals (x = 0.01 – 0.25) are grown and studied for their ferromagnetic properties. A new oxide phase Ba₂Eu₂P₂O (P4/mbm #127, Z = 2) has also been synthesized from the same method, and may potentially be studied as a ferromagnetic semiconductor based on preliminary observations. Other examples of single crystal oxide phases grown from barium metal flux includes Ba₂TeO (P4/nmm #129, Z = 2), BaLn₂O₄(Ln = La – Lu) (Pnma #62, Z = 4), and Ba₃Yb₂O₅Te (P4/mmm #123 Z = 1). The new crystal phases Ba₃Ln₂O₅Cl₂ (Ln = Sm – Lu, Y) are synthesized using a reactive barium metal flux. Single crystal x-ray diffraction is used to determine their structures with space group (I4/mmm #139, Z = 2) related to the Ruddlesden-Popper structure type. The unit cell dimensions range from a = 4.46(6) Å and c = 24.87(6) Å for Ba₃Gd₂O₅Cl₂ to a = 4.35(6) Å and c = 24.57(6) Å for Ba₃Lu₂O₅Cl₂ with the dimensions following the expected lanthanide contraction trends. The magnetic properties of these materials are studied and related to their structures. The use of alkaline earth fluxes such as magnesium or calcium based fluxes are also briefly considered for their capabilities to produce novel mixed anion phases. A calcium flux is shown to produce the novel semimetals Ca₄TeOH₄ and Ca₃Ca₁₋xEuxTeOH₄ (I4/mmm #139, Z = 2), and highly reducing magnesium fluxes are shown to produce the divalent samarium Zintl phases SmMg₂Bi₂ and SmMg₂Sb₂ (P3m1 #163, Z = 1).
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Date Issued: 2016
Identifier: FSU_2016SU_Ramirez_fsu_0071N_13312
Format: Thesis

Title: Nuclear Structure Studies of ¹⁹O, ²⁷Mg, and ²⁹Al Using in-Beam γ-Ray Spectroscopy.
Creator: Dungan, Rutger, Tabor, Samuel Lynn, Humayun, Munir, Riley, Mark A., Volya, Alexander, Prosper, Harrison B., Florida State University, College of Arts and Sciences, Department of...
Show moreDungan, Rutger, Tabor, Samuel Lynn, Humayun, Munir, Riley, Mark A., Volya, Alexander, Prosper, Harrison B., Florida State University, College of Arts and Sciences, Department of Physics
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Abstract/Description: This dissertation reports the study of three nuclei ¹⁹O, ²⁹Al, and ²⁷Mg at high angular momentum using ɣ-ray spectroscopy. These experiments were performed at the John D. Fox Superconducting Linear Accelerator at Florida State University (FSU). ɣ-radiation and charged particles were detected in coincidence by employing the Compton suppressed FSU ɣ-detector array in conjunction with a silicon ΔE-E particle telescope. The ⁹Be(¹⁴C, ɑɣ) reaction at beam energies of 30 and 35 MeV were used to...
Show moreThis dissertation reports the study of three nuclei ¹⁹O, ²⁹Al, and ²⁷Mg at high angular momentum using ɣ-ray spectroscopy. These experiments were performed at the John D. Fox Superconducting Linear Accelerator at Florida State University (FSU). ɣ-radiation and charged particles were detected in coincidence by employing the Compton suppressed FSU ɣ-detector array in conjunction with a silicon ΔE-E particle telescope. The ⁹Be(¹⁴C, ɑɣ) reaction at beam energies of 30 and 35 MeV were used to populate excited levels of ¹⁹O. The data were sorted for α-ɣ and α-ɣ-ɣ coincidences. A total of eight new ɣ transitions and the addition of one new state in ¹⁹O were identified. Six of these ɣ transitions correspond to neutron unbound states. These results are compared to shell model calculations using the USDA, WBP, and PSDU interactions. The neutron unbound ɣ decaying states are best identified with states having higher spin and small spectroscopic factors. Excited levels were populated in ²⁹Al and ²⁷Mg using the reactions ¹⁸O(¹⁴C,p2n) and ¹⁸O(¹⁴C,α n) at 40 MeV. The data were sorted for p-ɣ-ɣ and α-ɣ-ɣ coincidences for ²⁹Al and ²⁷Mg respectively. The level and decay schemes of both nuclei have been expanded with the addition of several new levels and electromagnetic transitions. The results for both nuclei are compared to shell model calculations using the USDA and WBP interactions.
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Date Issued: 2016
Identifier: FSU_2016SU_Dungan_fsu_0071E_13358
Format: Thesis

Title: Lipid-Protein Interactions Defined by Multi-Frequency EPR: Examples from HIV-1 Envelope and Antimicrobial Peptides.
Creator: Pavanjeet Kaur, FNU, Song, Likai, Hill, S. (Stephen Olof), Cross, Timothy A., Rikvold, Per Arne, Van Winkle, David H., Piekarewicz, Jorge, Florida State University, College of...
Show morePavanjeet Kaur, FNU, Song, Likai, Hill, S. (Stephen Olof), Cross, Timothy A., Rikvold, Per Arne, Van Winkle, David H., Piekarewicz, Jorge, Florida State University, College of Arts and Sciences, Department of Physics
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Abstract/Description: Electron paramagnetic resonance (EPR) spectroscopy is a powerful tool to elucidate the structure and dynamics of membrane proteins and protein-lipid interactions. High magnetic fields increase EPR sensitivity and broaden its practice through increased time scale and g-tensor resolution. However, the application of high-field EPR is hindered by the lack of suitable techniques and methodologies. The focus of this work is to develop high-field and multi-frequency EPR methods for characterizing...
Show moreElectron paramagnetic resonance (EPR) spectroscopy is a powerful tool to elucidate the structure and dynamics of membrane proteins and protein-lipid interactions. High magnetic fields increase EPR sensitivity and broaden its practice through increased time scale and g-tensor resolution. However, the application of high-field EPR is hindered by the lack of suitable techniques and methodologies. The focus of this work is to develop high-field and multi-frequency EPR methods for characterizing membrane proteins, with specific aims to investigate lipid-protein interactions of an antibacterial peptide (AA1) and HIV-1 envelope protein gp41. These methods include: i). A thin-layer cylindrical sample holder designed for studying low-yield biological samples at 94 GHz (W-band). The holder is non-resonant and operating in induction-mode for continuous wave EPR analyses. A concentration sensitivity of 2 µM was achieved for a spin-label standard and 20-30 µM for the biological aqueous samples, representing a ~10-fold enhancement compared to a cylindrical TE₀₁₁ resonator on a commercial Bruker W-band spectrometer (Chapter 3). ii). Magnetic alignment of cholesterol-containing bicelles at high fields. Membranes with high cholesterol content are typical in mammalian cells and are important for biophysical studies mimicking native conditions, such as using aligned bicelles to study protein orientation in membranes. In this study, field dependence of magnetic alignment of cholesterol-containing bicelles was investigated and enhanced bicelle alignment at high fields were demonstrated (Chapter 5). Other EPR techniques developed here include: 1) Membrane permeability analysis to assess membrane disruption by proteins; 2) Lipid lateral ordering induced by protein binding defined using EPR at 94 GHz; 3) A new application of EPR power saturation methods to determine membrane thinning. These EPR techniques were applied to define the molecular basis of the antimicrobial activity of AA1. The results show that the peptide selectively permeates and structurally modifies negatively charged bacterial-mimic membranes. In contrast, cholesterol-containing neutral membranes mimicking mammalian cells were minimally affected by the molecule. Based on combined EPR analyses, we proposed a “carpet-like” mechanism for the antimicrobial activities of AA1. The results provide implications for the development of effective AMPs with robust antibacterial activities against antibiotic-resistant microbes (Chapter 4). Additionally, magnetic alignment of bicelles was used to study the membrane bound region (MPERTM) of HIV-1 envelope protein gp41. Using a rigid spin-label–TOAC, the structural information of the MPERTM in membranes was determined by studying backbone dynamics, immersion depths and helical tilt in bicelles. The results indicate the existence of three separated helical segments of the MPERTM with different motional time-scales. The effect of lipid composition and cholesterol content on the conformation of the MPERTM in the membrane were also investigated (Chapter 6). In summary, we have demonstrated and further developed the applications of multi-frequency and high-field EPR in studying membrane proteins and lipid-protein interactions.
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Date Issued: 2016
Identifier: FSU_2016SU_Pavanjeetkaur_fsu_0071E_13131
Format: Thesis

Title: Spin Transport and Nanomagnetism in Semiconductor Heterostructures.
Creator: Kim, Joon-Il, Xiong, Peng, Mattoussi, Hedi, Bonesteel, N. E., Van Winkle, David H., Florida State University, College of Arts and Sciences, Department of Physics
Abstract/Description: Semiconductor spintronics is widely regarded as a viable pathway to overcome many of the physical limitations of the present micro-electronics technology. Electrical spin injection into a semiconductor, coherent transport and manipulation of the injected spins in the semiconductor channel, and detection of the transported spins via another probe are indispensable ingredients of the proposed spin-based field effect transistors (spin-FETs), which may offer transformative new functionalities not...
Show moreSemiconductor spintronics is widely regarded as a viable pathway to overcome many of the physical limitations of the present micro-electronics technology. Electrical spin injection into a semiconductor, coherent transport and manipulation of the injected spins in the semiconductor channel, and detection of the transported spins via another probe are indispensable ingredients of the proposed spin-based field effect transistors (spin-FETs), which may offer transformative new functionalities not present in a conventional FET. The primary goal of this dissertation is to study spin transport and understand the spin dynamics in a semiconductor. A most unique aspect of this research is the use a persistent photoconductor, Si-doped Al₀.₃.3Ga₀.₇As, as the spin transport channel material. Utilizing the persistent photoconductivity of Al₀.₃.3Ga₀.₇As:Si, we can tune the carrier density of the spin channel in the device in situ by photo-doping, spanning a broad range from the insulating to metallic state. This facilitates investigation of the spin accumulation and transport properties on one and the same sample over orders of magnitude variation in the carrier density in the spin channel. Exploitation of the persistent photoconductivity circumvents the issues that arise when using multiple samples; we significantly reduce fabrication time required to make many replicas at differing doping levels, and more importantly, avoid sample-to-sample variations influencing the measurements. 3-terminal (3T) and nonlocal 4-terminal (4T) Hanle measurements have been performed on our lateral devices with patterned Fe electrodes for spin injection and detection, and Al₀.₃.3Ga₀.₇As:Si as the spin transport channel. The measurements were conducted over a broad range of carrier densities across the insulator-to-metal transition (IMT). The bias current and channel carrier density dependencies of 3T and nonlocal 4T Hanle signals have been measured and systematically compared. Although their magnitudes differ by about an order of magnitude, the 3T and nonlocal 4T Hanle signals exhibit broad similarities in many aspects, including their dependencies on the carrier density and bias current. The specific resistance of the injecting junction plays a very important role in spin injection/extraction between a ferromagnet and semiconductor. Using the measured channel resistivity and junction specific resistance, the experimentally obtained Hanle signal magnitudes could be compared with the expectations based on spin accumulation in the theoretical framework of Fert and coworkers. In our devices with an interface of epitaxial graded Schottky junctions, the 3T Hanle magnitudes are in general agreement with the theoretical expectations. Specifically, the experimental values are smaller than the theoretical expectation in the insulating state, attain good agreement in the vicinity of the IMT, and become greater than the theoretical values by several factors deep into the metallic state. The observed discrepancies away from the IMT in our devices should be contrast with the results in spin devices with oxide tunnel barriers, where the 3T Hanle signals are often several orders of magnitude greater than the theoretical predictions. Furthermore, in our devices, the 3T Hanle signals are consistent with an exponential spatial decay of the spin accumulation based on the nonlocal 4T Hanle measurements. The spin lifetimes in the AlGaAs channel are determined from the 3T and nonlocal 4T Hanle curves, via separate fits to the Lorentzian function and the one dimensional spin drift-diffusion model. The two approaches yield similar values of spin lifetime, from 2 to 4 ns, and similar evolution with the carrier density. This comprehensive set of measurements covering large ranges of carrier density and bias current revealed broad and striking similarities between the 3T and nonlocal 4T Hanle signals in our devices. The results provide strong evidence that the 3T Hanle measurements in devices structures like ours with an epitaxial Schottky junction are indeed manifestation of spin accumulation, rather than due to other spurious effects. The research has shed considerable light on a number of pertinent issues in spin relaxation and spin transport in semiconductors. The second line of research of this dissertation is to utilize the high-sensitivity semiconductor Hall magnetometry techniques to study the static and dynamic magnetic properties of InAs quantum dots (QDs) doped with Cr or Mn. The goal of this research was to measure the magnetization of a small array of, or even an individual, QDs via an integrated micro/nano Hall magnetometer based on the 2-dimensional electron gas (2DEG) GaAs/AlGaAs heterostructure. The experiment was expected to facilitate a direct correlation of the measured magnetic properties of the QDs with their structural/chemical characteristics, which may provide insight on the fundamentally important issue of the origin of ferromagnetism in diluted magnetic semiconductors. A fabrication procedure was developed, which produced devices enabling Hall gradiometry measurements. However, due to the persistent difficulty of producing ohmic contacts to the 2DEG while limiting the sample temperature, the signal-to-noise ratio of the devices was not adequate for measuring the magnetization of the QDs.
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Date Issued: 2016
Identifier: FSU_2016SU_KIM_fsu_0071E_13318
Format: Thesis

Title: Impurities and Defects in Mott Systems.
Creator: Tang, Shao, Dobrosavljević, Vladimir, Shatruk, Mykhailo, Xiong, Peng, Bonesteel, N. E., Okui, Takemichi, Florida State University, College of Arts and Sciences, Department of...
Show moreTang, Shao, Dobrosavljević, Vladimir, Shatruk, Mykhailo, Xiong, Peng, Bonesteel, N. E., Okui, Takemichi, Florida State University, College of Arts and Sciences, Department of Physics
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Abstract/Description: Disorder has intriguing consequences for correlated electronic materials, which include several families of high-temperature superconductors and resistive switching systems. In this dissertation, we study the effects of impurities intertwined with correlations. First, we study impurity healing effects in models of strongly correlated superconductors. We show that in general both the range and the amplitude of the spatial variations caused by nonmagnetic impurities are significantly suppressed...
Show moreDisorder has intriguing consequences for correlated electronic materials, which include several families of high-temperature superconductors and resistive switching systems. In this dissertation, we study the effects of impurities intertwined with correlations. First, we study impurity healing effects in models of strongly correlated superconductors. We show that in general both the range and the amplitude of the spatial variations caused by nonmagnetic impurities are significantly suppressed in the superconducting as well as in the normal states. We explicitly quantify the weights of the local and the non-local responses to inhomogeneities and show that the former are overwhelmingly dominant over the latter. We find that the local response is characterized by a well-defined healing length scale, which is restricted to only a few lattice spacings over a significant range of dopings in the vicinity of the Mott insulating state. We demonstrate that this healing effect is ultimately due to the suppression of charge fluctuations induced by Mottness. We also define and solve analytically a simplified yet accurate model of healing, within which we obtain simple expressions for quantities of direct experimental relevance. Second, we address the question of why strongly correlated d-wave superconductors, such as the cuprates, prove to be surprisingly robust against the introduction of non-magnetic impurities. We show that, very generally, both the pair-breaking and the normal state transport scattering rates are significantly suppressed by strong correlations effects arising in the proximity to a Mott insulating state. We also show that the correlation-renormalized scattering amplitude is generically enhanced in the forward direction, an effect which was previously often ascribed to the specific scattering by charged impurities outside the copper-oxide planes. Finally, we provide the theoretical insights for resistive switching systems and show how impurities and underlying correlations can play significant roles in practical devices. We report the striking result of a connection between the resistive switching and shock wave formation, a classic topic of non-linear dynamics. We argue that the profile of oxygen vacancies that migrate during the commutation forms a shock wave that propagates through a highly resistive region of the device. We validate the scenario by means of model simulations and experiments in a manganese-oxide based memristor device and we extend our theory to the case of binary oxides. The shock wave scenario brings unprecedented physical insight and enables to rationalize the process of oxygen-vacancy-driven resistive change with direct implications for a key technological aspect – the commutation speed.
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Date Issued: 2016
Identifier: FSU_2016SU_Tang_fsu_0071E_13282
Format: Thesis

Title: Experimental Investigation of On-Chip ESR Techniques in Multiple Temperature Regimes.
Creator: Zabalo, Aidan, Chiorescu, Irinel, Baumbach, Ryan Eagle, Capstick, Simon, Hill, S. (Stephen Olof), Florida State University, College of Arts and Sciences, Department of Physics
Abstract/Description: The underlying physics and spin dynamics that govern magnetic molecules yield ideal behavior for their potential use as qubits in a quantum computer. To characterize the spin dynamics of these magnetic molecules, electron spin resonance (ESR) techniques are often used. In this study, a method in which the use of superconducting quantum interference devices (SQUIDs) and vibrating sample magnetometry (VSM) technologies can be combined with traditional ESR measurements is explored. This was...
Show moreThe underlying physics and spin dynamics that govern magnetic molecules yield ideal behavior for their potential use as qubits in a quantum computer. To characterize the spin dynamics of these magnetic molecules, electron spin resonance (ESR) techniques are often used. In this study, a method in which the use of superconducting quantum interference devices (SQUIDs) and vibrating sample magnetometry (VSM) technologies can be combined with traditional ESR measurements is explored. This was achieved by modification of a commercial sample probe such that microwaves can effectively reach the sample under study. Additionally, the ability to tune the coupling parameter of a superconducting cavity is achieved through the use of temperature and magnetic field. This is of particular importance in on-chip ESR measurements and can be described by the losses in the device. This investigation describes a versatile setup which can be used to study a variety of magnetic molecules in multiple temperature regimes.
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Date Issued: 2016
Identifier: FSU_2016SP_Zabalo_fsu_0071N_13258
Format: Thesis

Title: A Study of 3Π Production in ΓP → NΠ+Π+Π− and ΓP → Δ++Π+Π−Π− with CLAS at Jefferson Lab.
Creator: Tsaris, Aristeidis, Eugenio, Paul Michael, Plewa, Tomasz, Crede, Volker, Capstick, Simon, Owens, Joseph F., Florida State University, College of Arts and Sciences, Department of...
Show moreTsaris, Aristeidis, Eugenio, Paul Michael, Plewa, Tomasz, Crede, Volker, Capstick, Simon, Owens, Joseph F., Florida State University, College of Arts and Sciences, Department of Physics
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Abstract/Description: Apart from the mesons that the constituent quark model predicts, QCD allows for additional states beyond the quark-antiquark system. Previous experiments have performed partial wave analysis on pion-production data and claim observation of an exotic JPC = 1−+ state decaying via ρπ. The g12 experiment took place at Jefferson Lab using the CLAS spectrometer, a liquid hydrogen target was used and a tagged photon beam. By studying the reactions γp → nπ+π +π − and γp → ∆++π +π −π −, the...
Show moreApart from the mesons that the constituent quark model predicts, QCD allows for additional states beyond the quark-antiquark system. Previous experiments have performed partial wave analysis on pion-production data and claim observation of an exotic JPC = 1−+ state decaying via ρπ. The g12 experiment took place at Jefferson Lab using the CLAS spectrometer, a liquid hydrogen target was used and a tagged photon beam. By studying the reactions γp → nπ+π +π − and γp → ∆++π +π −π −, the photoproduction of mesons decaying to 3π was studied using two different but complimentary channels. Events are selected with low four-momentum transfer to the baryon, in order to enhance one pion exchange production. For both 3π systems the data exhibit two intermediate decays, ρπ and f2π. For the γp → nπ+π +π − reaction over 600k events were acquired resulting in the largest 3π photoproduction dataset to date. The exotic JPC= 1−+ partial wave does not show resonant behavior and more so it is strongly consistent with a non-resonant non-interfering wave relative to a resonant π2(1670). Furthermore, the partial wave analysis shows production of the a2(1320) and π2(1670) mesons. For the first time we report observation of a photoproduced a1(1260) meson. For the γp → ∆++π +π −π − reaction nearly 350k events were analyzed. A partial wave analysis was performed for the first time on this channel. The a1(1260), a2(1320), and the π2(1670) mesons were observed. Observation of the a1(1260) confirms the result first reported in γp → nπ+π +π − reaction.
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Date Issued: 2016
Identifier: FSU_2016SP_Tsaris_fsu_0071E_13044
Format: Thesis

Title: Magnetic Phase Diagram of Triangular Lattice Antiferromagnet Ba₃MNb₂O9 (M = Co, Mn) and Its Multiferroicity.
Creator: Lee, Minseong, Choi, Eun Sang, Manousakis, Efstratios, Dalal, Naresh S., Chiorescu, Irinel, Crede, Volker, Florida State University, College of Arts and Sciences, Department of...
Show moreLee, Minseong, Choi, Eun Sang, Manousakis, Efstratios, Dalal, Naresh S., Chiorescu, Irinel, Crede, Volker, Florida State University, College of Arts and Sciences, Department of Physics
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Abstract/Description: This dissertation mainly focuses on the investigation of the magnetic phase diagram of quasi two di- mensional triangular lattice antiferromagnets (TLAFs) Ba₃MNb₂O9 (M = Co2+ (S = 1/2), Mn2+ (S = 5/2)), and their multiferroic properties. Both compounds show a two-step magnetic phase transition at TN1 and TN2 upon cooling from paramagnetic to up-up-down(uud) phase due to the easy-axis anisotropy, and 120 degree ordered phase at zero field. This feature is dissimilar to that of sister a...
Show moreThis dissertation mainly focuses on the investigation of the magnetic phase diagram of quasi two di- mensional triangular lattice antiferromagnets (TLAFs) Ba₃MNb₂O9 (M = Co2+ (S = 1/2), Mn2+ (S = 5/2)), and their multiferroic properties. Both compounds show a two-step magnetic phase transition at TN1 and TN2 upon cooling from paramagnetic to up-up-down(uud) phase due to the easy-axis anisotropy, and 120 degree ordered phase at zero field. This feature is dissimilar to that of sister a compound Ba₃MNb₂O9 (Ni2+, (S = 1)), in which a single magnetic phase transition occurs due to the easy-plane anisotropy at zero field. Moreover, at low temperature below TN1, successive magnetic phase transitions were observed in both compounds. However, in case of Co compounds, the range of magnetic field where the uud phase stabilizes becomes wider at lower temperature whereas becomes narrower in case of Mn compounds. This different behavior is originated from the nature of the fluctuations that stabilize the uud phase, that is, quantum and/or classical fluctuations. We also found that the spin magnitude and spin structure play a crucial role in stabilizing the multiferroic ground state. Multiferroicity appears in all magnetically ordered phase in the small-spin-system Co compound but only in 120 degree ordered state in the large-spin-system Mn compound. The systematic studies on these compounds provide a highly valuable playground in the investigate of the effect of spin varied from 1/2 to 5/2 in frustrated magnets and multiferroics, attract many interests and in the field.
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Date Issued: 2016
Identifier: FSU_2016SP_Lee_fsu_0071E_13120
Format: Thesis

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