Current Search: Piekarewicz, Jorge (x)
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 Title
 Fabrication and Characterization of Heterogeneous Nanowires.
 Creator

Barreda Esparza, Jorge Luis, Xiong, Peng, Guan, Jingjiao, Bonesteel, N. E., Chiorescu, Irinel, Piekarewicz, Jorge, Florida State University, College of Arts and Sciences,...
Show moreBarreda Esparza, Jorge Luis, Xiong, Peng, Guan, Jingjiao, Bonesteel, N. E., Chiorescu, Irinel, Piekarewicz, Jorge, Florida State University, College of Arts and Sciences, Department of Physics
Show less  Abstract/Description

Nanoscience and nanotechnology research has provided us with new paradigms of technologies to improve human life, but still there is plenty of room to expand its frontiers. In order to do so, we need to pursue the development and study of novel nanostructures with the main goal of understanding the physical properties and finding potential applications. Understanding the physics of lowdimensional systems is the first step to fostering the corresponding technological applications. Considering...
Show moreNanoscience and nanotechnology research has provided us with new paradigms of technologies to improve human life, but still there is plenty of room to expand its frontiers. In order to do so, we need to pursue the development and study of novel nanostructures with the main goal of understanding the physical properties and finding potential applications. Understanding the physics of lowdimensional systems is the first step to fostering the corresponding technological applications. Considering this premise, the goal of this dissertation is to study two distinct classes of heterogeneous nanowires (NWs): phosphorousdoped Si NWs with an axial doping gradient and metal NWs grown on DNA templates. The Si NWs grown by vaporliquidsolid chemical vapor deposition were utilized to fabricate Schottky barrierlimited fieldeffect transistors (FETs), which have shown significant promise in the areas of electronics and sensing because of their unique characteristics. The idea of utilizing the modulation of the nano Schottky junction at a metalsemiconductor interface promises higher performance for chemical and biomolecular sensor applications when compared to conventional FETs with Ohmic contacts (exponential versus linear responses). However, the fabrication of such asymmetric FETs presents challenges such as reproducibility through complications in the fabrication processes. We have been able to circumvent the fabrication difficulties and reproducibility problems by utilizing our Si nanowires synthesized by a chemical vapor deposition process which yields a pronounced doping gradient along the length of the NWs. This inhomogenous doping in NWs has typically been seen as a detrimental characteristic; however, we have taken advantage of this doping profile as the basis of our approach. The graded doping profile facilitates definition of a series of metal contacts on a single NW that systematically evolve from Ohmic to Schottky with increasing effective barrier height along the axial direction. The study of this systematic variation is presented in this dissertation as a proposal to obtain devices for sensing and electronic applications. The main results of our research is recently published. The fabrication and study of metal NWs is the second effort discussed in this dissertation. The main motivation is to address the fundamental question of whether a true superconducting state could exist in one dimension. The answer to this question lies in the nature of superconducting fluctuations of the order parameter that describe the coherent behavior of the Cooper pairs. In a superconducting system, the order parameter has a welldefined amplitude and phase. The superconducting fluctuations occur in the form of phase slips which can be either thermally activated or quantum mechanical. Although much experimental and theoretical work has been done on the topic, an unambiguous resolution of this issue remains elusive mainly due to the challenge of producing NWs having the dimensions of the crosssection of the NW smaller than the superconducting coherence length or the size of the Cooper pairs. Our approach to overcome the fabrication difficulties to reach the true 1D limit is a unique combination of DNA templates and low temperature quenchcondensation for in situ fabrication and measurement of superconducting NWs with a width of just a few nanometers. In this dissertation, details on the fabrication and our initial results demonstrating the capability of our DNA molecular templates to reach small crosssection metal NWs are presented; also, we present systematic characterizations of the electrical properties of metal nanowires with respect to in situ variation of the geometry of the nanowire. This effort has laid a full foundation for a comprehensive examination of superconductivity in 1D reaching unprecedentedly small crosssections. A manuscript summarizing these results is in preparation.
Show less  Date Issued
 2017
 Identifier
 FSU_2017SP_Barreda_fsu_0071E_13848
 Format
 Thesis
 Title
 Pairing Correlations and Phase Transitions in Mesoscopic Systems.
 Creator

Sumaryada, Tony Ibnu, Volya, Alexander, Li, Hong, Piekarewicz, Jorge, Rogachev, Grigory, Dobrosavljevic, Vladimir, Department of Physics, Florida State University
 Abstract/Description

Pairing correlations and phase transitions in mesoscopic or small systems are studied through out this dissertation. We start our discussion by showing the importance of short range correlations and their role in forming bound Cooper pairs. For a model Hamiltonian, we solved the Schr¨odinger equation in the harmonic oscillator basis analytically, the concept of self consistency is used to get the whole energy spectrum. Using variational methods applied to a trial wave function, we derived the...
Show morePairing correlations and phase transitions in mesoscopic or small systems are studied through out this dissertation. We start our discussion by showing the importance of short range correlations and their role in forming bound Cooper pairs. For a model Hamiltonian, we solved the Schr¨odinger equation in the harmonic oscillator basis analytically, the concept of self consistency is used to get the whole energy spectrum. Using variational methods applied to a trial wave function, we derived the BCS equations, which again should be solved self consistently with particle number to produce the total energy. Some examples of BCS calculations in realistic case like in the Sn isotopes are shown. Various approximations such as one level, two levels and five levels systems are discussed. In the five levels model calculations, we compare our results with the previous works by other authors. We also find a good agreement with the experimental data. We extend our BCS calculations by adding the three body interaction term. This additional term is unlikely to improve our results compared to the experiment. In a separate work, using numerical and analytical methods implemented for different models we conduct a systematic study of thermodynamic properties of pairing correlations in mesoscopic nuclear systems. Various quantities are calculated and analyzed using the exact solution of pairing. An indepth comparison of canonical, grand canonical, and microcanonical ensemble is conducted. The nature of the pairing phase transition in a small system is of particular interest. We discuss the onset of discontinuities in the thermodynamic variables, fluctuations, and evolution of zeros of the canonical and grand canonical partition functions in the complex plane. The behavior of the Invariant Correlational Entropy is also studied in the transitional region of interest. The change in the character of the phase transition due to the presence of magnetic field is discussed along with studies of superconducting thermodynamics.
Show less  Date Issued
 2007
 Identifier
 FSU_migr_etd0406
 Format
 Thesis
 Title
 Structural Behavior of 157,158,159Dy in the I=30−50L Spin Regime and the HighSpin Domain of 158Er Up to and Above Band Termination.
 Creator

Pipidis, Paschalis Akis, Riley, Mark A., Aldrovandi, Ettore, Piekarewicz, Jorge, Reina, Laura, Eugenio, Paul M., Department of Physics, Florida State University
 Abstract/Description

The question of how do the properties of nuclei evolve with increasing excitation energy and angular momentum is one of the current frontiers in nuclear physics. State of the art $gamma$ray detector systems have been used to investigate this question, in a series of rareearth nuclei with mass extit{A}$sim$158. Significant extensions to the highspin excitation spectrum of the $N$=91, 92, 93 isotopes $^{157,158,159}$Dy have been achieved using the highefficiency $gamma$ray spectrometers...
Show moreThe question of how do the properties of nuclei evolve with increasing excitation energy and angular momentum is one of the current frontiers in nuclear physics. State of the art $gamma$ray detector systems have been used to investigate this question, in a series of rareearth nuclei with mass extit{A}$sim$158. Significant extensions to the highspin excitation spectrum of the $N$=91, 92, 93 isotopes $^{157,158,159}$Dy have been achieved using the highefficiency $gamma$ray spectrometers EUROBALL and GAMMASPHERE. These nuclei were populated via weak 3$n$ or $alpha xn$ exit channels in fusion evaporation reactions. In $^{157}$Dy, the yrast band has been extended to extit{I}$^pi$=$frac{101}{2}^{+}$ (tentatively to $frac{105}{2}^{+}$) with four sideband structures (two of which are new) observed in the 35$$50 $hbar$ spin range. In $^{158}$Dy, three bands have been extended to 42$^{+}$ (44$^{+}$), 40$^{}$, and 41$^{}$ (43$^{}$), while in $^{159}$Dy the yrast band is observed to $frac{81}{2}^{+}$ ($frac{85}{2}^{+}$). A total of 84 (99) new transitions, including 2 new bands, were added to the level schemes of $^{157,158,159}$Dy. The highspin behavior and band crossing systematics of the Dy isotopes and of the neighboring $N$=91, 92, and 93 isotones are discussed in terms of rotational alignments and shape transitions. Cranked NilssonStrutinsky calculations without pairing have been performed for detailed comparisons with the very highspin states observed in $^{157}$Dy. Results on $^{157,158,159}$Dy have been published in extit{Phys. Rev. C.} Moreover, the angularmomentum induced transition from a deformed state of collective rotation to a noncollective configuration has been studied. In $^{158}$Er this transition manifests itself as favored band termination near extit{I}$approx$45$hbar$. The feeding of these band terminating states has been investigated for the first time using the GAMMASPHERE spectrometer. A large number of weakly populated states, lying at high excitation energy, that decay into these special states have been discovered. Cranked NilssonStrutinsky calculations suggest that these states arise from weakly collective configurations that break the $Z$=64 semimagic core. Additionally, a new frontier of discreteline $gamma$ray spectroscopy at ultrahigh spin has been opened in the rareearth nucleus $^{158}$Er. Two rotational structures, displaying high moments of inertia, have been identified, which extend up to spin $sim$65$hbar$ and bypass the bandterminating states in these nuclei near extit{I}$sim$45$hbar$. Cranked NilssonStrutinsky calculations suggest that these structures arise from welldeformed triaxial configurations that lie in a valley of favored shell energy, which also includes the wellknown triaxial strongly deformed bands in $^{161167}$Lu. Overall, 182 (209) new transitions, including 10 new bands, were placed in the greatly augmented level scheme of $^{158}$Er, as a result of our work in this thesis. Four of the new bands are based on high$$ extit{K} quasiparticle excitations, which provide a stringent test of the Cranked Shell Model. This enables the investigation and interpretation of many different quasiparticle configurations from their alignment properties and band crossings systematics. Results on $^{158}$Er have been published in extit{Phys. Rev. Lett.} and extit{Phys. Scr.} Finally, a local experiment, using the FSU tandem accelerator and the FSU $gamma$ray detectors, was performed to investigate the oddodd nucleus $^{158}$Tb. Unfortunately, no new significant results on the latter were obtained except for the tentative assignment of a new, stronglycoupled, rotational structure.}
Show less  Date Issued
 2006
 Identifier
 FSU_migr_etd0687
 Format
 Thesis
 Title
 Studies of Novel Magnetic Materials and Interfaces via Electronic Transport and Superconducting Spectroscopy.
 Creator

Zhang, Xiaohang, Xiong, Peng, Dalal, Naresh, Molnár, Stephan von, Vafek, Oskar, Piekarewicz, Jorge, Department of Physics, Florida State University
 Abstract/Description

The exploration of new paradigms for micro and nanoelectronics has engendered several exciting new research fields including molecular electronics and spintronics. Two essential ingredients of the device structures are materials and interfaces. The overarching theme of this dissertation is the study of the (spindependent) electronic states and transport in novel magnetic materials and through molecular interfaces. These experiments are necessary first steps in ascertaining potential...
Show moreThe exploration of new paradigms for micro and nanoelectronics has engendered several exciting new research fields including molecular electronics and spintronics. Two essential ingredients of the device structures are materials and interfaces. The overarching theme of this dissertation is the study of the (spindependent) electronic states and transport in novel magnetic materials and through molecular interfaces. These experiments are necessary first steps in ascertaining potential utilities in molecular electronic and spintronics applications. More importantly for this thesis, the materials and hybrid device structures provide a fertile ground for studying basic physics of magnetism, magnetotransport, and spin transport. In this dissertation, various techniques of superconducting spectroscopy have been used to investigate the spindependent electronic density of states of the thiol/Au molecular interface and the ferromagnetic semimetal EuB6. In addition, a fresh analysis of the electronic transport properties of EuB6 reveals a new type of nonlinear Hall effect intimately related to its magnetic state and culminates in a model that offers excellent quantitative understanding of the data and appears applicable to a wide varieties of magnetic materials. In order to directly probe possible induced magnetism at the thiolgold interface, spin polarized tunneling measurements were performed on planar tunnel junctions incorporating a molecular monolayer of mercaptohexadecanoic acid [HS(CH2)15COOH] (MHA) between aluminum and gold electrodes. The Zeeman resolved tunneling spectra yield no measurable spin polarization at the thiolgold interface, contrary to the expectations from the reported induced giant magnetic moments at the interface. On the other hand, variations in the resistance of the fabricated tunnel junctions with changing environmental conditions were consistently observed. A systematic investigation revealed that the effect is directly linked to the interaction of water molecules with the carboxylate groups of the MHA monolayer at the AlOx surface. Analyses of the IV characteristics produce compelling evidence for significant modifications of the tunnel barrier height of the AlOx upon adsorption of the MHA monolayer, and subsequently by the reaction of water molecules with the carboxylate group at the AlOx surface. The results demonstrate that environmental effects could significantly impact the electron transport even in molecular junctions of macroscopic dimensions and closed architecture. Andreev reflection spectroscopy measurements performed on junctions consisting of EuB6 single crystals and lead electrodes clearly demonstrated that EuB6 is not a half metal with a fully spin polarized Fermi surface. Instead, the measured spin polarization values range from 47% to 65%. Analyses based on the measured spin polarization together with Fermi surface and transport measurements lead to a quantitatively consistent picture in agreement with a semimetallic band structure with a substantial band splitting for the valence band only in the ferromagnetic phase. Moreover, the analyses also indicate a semimetallic band structure with localized holes in the paramagnetic phase and a delocalization of the holes near ferromagnetic ordering. Our studies on EuB6 provide important clarification of its spin dependent band structure. Hall effect and magnetoresistance measurements were also performed on EuB6 single crystals. The data are consistent with previous reports. However, we offer a new analysis of the Hall effect which has led to significant new insights. An unusual change in the Hall resistivity slope with increasing magnetic field was observed in the paramagnetic phase. The change in Hall resistivity slope was found to occur at a universal critical magnetization at all temperatures. A twocomponent model based on a picture of intrinsic (nonchemical) electronic/magnetic inhomogeneities and coalescing of a phase with higher conductivity and degree of magnetic ordering was proposed to fit the observed Hall effect. Excellent quantitative agreement was obtained and with this model all the Hall resistivity data were scaled onto a single curve. Significantly, this model and picture were found to offer consistent description of the nonlinear Hall effect in a diverse group of magnetic materials including the mixed valence perovskites and the heavy fermion metal YbRh2Si2. The results indicate that this may be a common form of Hall effect associated with percolative magnetic phase transitions.
Show less  Date Issued
 2008
 Identifier
 FSU_migr_etd0540
 Format
 Thesis
 Title
 Numerical Study of SpinFermion Models for Diluted Magnetic Semiconductors and High Tc Cuprates.
 Creator

Yildirim, Yucel, Bonesteel, Nicholas E., Dalal, Naresh, Vafek, Oskar, Piekarewicz, Jorge, Xiong, Peng, Department of Physics, Florida State University
 Abstract/Description

In this dissertation, SpinFermion (SF) models for diluted magnetic semiconductors and high temperature superconducting cuprates are constructed and studied with unbiased numerical techniques. A microscopic model to describe magnetically doped IIIV semiconductors is proposed. This model includes the appropriate lattice geometry, as well as, magnetic, spinorbit, and Coulomb interactions and contains no free parameters. Its study using stateoftheart numerical techniques provides results in...
Show moreIn this dissertation, SpinFermion (SF) models for diluted magnetic semiconductors and high temperature superconducting cuprates are constructed and studied with unbiased numerical techniques. A microscopic model to describe magnetically doped IIIV semiconductors is proposed. This model includes the appropriate lattice geometry, as well as, magnetic, spinorbit, and Coulomb interactions and contains no free parameters. Its study using stateoftheart numerical techniques provides results in excellent agreement with experimental data for Mn doped GaAs. For the first time, CurieWeiss behavior of the magnetization is obtained numerically and the values of the Curie temperature are reproduced in a wide range of Mn doping and compensations. We observed that for x (> or = to )3%, the holes are doped into the valence band and uniformly distributed in the material. This could support the "valence band" scenario regarding this material. Phononic degrees of freedom, which are often neglected in studies of high T or = to )3%, the holes are doped into the valence band and uniformly distributed in the material. This could support the "valence band" scenario regarding this material. Phononic degrees of freedom, which are often neglected in studies of high Tc cuprates, are considered in a numerical study of a spinfermion model. Both diagonal and offdiagonal electronphonon interactions are considered. While diagonal terms tend to stabilize ordered structures such as stripes, the offdiagonal terms introduce disorder making this structures more dynamical. Our results indicate that phonons play a role in the stabilization of stripelike states.
Show less  Date Issued
 2007
 Identifier
 FSU_migr_etd0668
 Format
 Thesis
 Title
 Numerical Study of the Relevance of Clustered States in Diluted Magnetic Semiconductors and High Temperature Superconductors.
 Creator

Alvarez, Gonzalo, Dagotto, Elbio, Dalal, Naresh, Moreo, Adriana, Brooks, James, Piekarewicz, Jorge, Department of Physics, Florida State University
 Abstract/Description

Several models for materials of much current interest in condensed matter physics have been numerically studied, using unbiased methods, including Monte Carlo simulations and exact treatment of the fermionic trace at finite temperature. It was found that many of these materials share common phenomenological aspects due to the presence of intrinsic inhomogeneities in the form of "clustered states". Some of these states are highly susceptible to external perturbations. The list includes diluted...
Show moreSeveral models for materials of much current interest in condensed matter physics have been numerically studied, using unbiased methods, including Monte Carlo simulations and exact treatment of the fermionic trace at finite temperature. It was found that many of these materials share common phenomenological aspects due to the presence of intrinsic inhomogeneities in the form of "clustered states". Some of these states are highly susceptible to external perturbations. The list includes diluted magnetic semiconductors and high temperature superconducting cuprates among others.
Show less  Date Issued
 2004
 Identifier
 FSU_migr_etd0027
 Format
 Thesis
 Title
 Yukawa Unification in SO(10) Susy Guts.
 Creator

Auto, Daniel M., Baer, Howard, Hunter, Christopher, Reina, Laura, Prosper, Harrison, Piekarewicz, Jorge, Department of Physics, Florida State University
 Abstract/Description

Supersymmetric grand unified models based on the SO(10) gauge group are especially attractive in light of recent data on neutrino masses. The simplest SO(10) SUSY GUT models predict unification of third generation Yukawa couplings (t –b – Ƭ) in addition to the usual gauge coupling unification. An assessment of the viability of such Yukawa unified models is presented. For the superpotential Higgs mass parameter μ>0, it is found that unification to less than 1% is possible, but only for GUT...
Show moreSupersymmetric grand unified models based on the SO(10) gauge group are especially attractive in light of recent data on neutrino masses. The simplest SO(10) SUSY GUT models predict unification of third generation Yukawa couplings (t –b – Ƭ) in addition to the usual gauge coupling unification. An assessment of the viability of such Yukawa unified models is presented. For the superpotential Higgs mass parameter μ>0, it is found that unification to less than 1% is possible, but only for GUT scale scalar mass parameter m16 ~ 8 – 20 TeV, and small values of gaugino mass m1/2 ≤ 150 GeV. Such models require tha a GUT scale mass splitting exists amongst Higgs scalars with m2Hu < m2Hd. Viable solutions lead to a radiatively generated inverted scalar mass hierarchy, with third generation and Higgs scalars being lighter than other sfermions. These models have a very heavy sfermions, so that unwanted flavor changing and CP violating SUSY processes are suppressed, but may suffer from some finetuning requirements. While the generated spectra satisify b → sγ and (g – 2)μ constraints, there exists tension with the dark matter relic density unless m16 ≤ 3TeV. These models offer prospects for SUSY discovery at the Fermilab Tevatron collider via the search for W1Z2 → 3l events, or via gluino pair production. If μ < 0, Yujawa coupling unification to less than 5% can occur for m16 and m 1/2≥ 1 – 2 TeV. Consistency of negative μ Yukawa unified models with b → sγ, (g – 2)μ, and relic density Ωh2 all imply very large values of m1/2 typically greater than about 2.5 TeV, in which case direct dection of sparticles may be a challenge even at the LHC. To address the tension between Yukawa unification and the excess of dark matter that the μ>0 models tend to predict, a couple of possible improvements are surveyed. One solution lowering the GUT scale mass value of first and second generation scalars, leads to uR and cR squark masses in the 90 – 120 GeV regime, which should be accessible to Fermilab Tavatron experiments. Another possibility is relaxing gaugino mass universality which may solve the relic density problem by having neutralino annihilations via the Z or h resonances, or by having a winolike LSP.
Show less  Date Issued
 2004
 Identifier
 FSU_migr_etd0037
 Format
 Thesis
 Title
 Dynamical Studies of Antiferromagnetic Exchange Interactions in Low Dimensional Quantum Spin Systems.
 Creator

De Lia, Anthony F., Dagotto, Elbio, Heil, Wolfgang, Moreo, Adriana, Piekarewicz, Jorge, Riley, Mark, Department of Physics, Florida State University
 Abstract/Description

Various forms of antiferromagnetic exchange interaction among quantized spins in onedimensional and quasionedimensional lattices are examined. Primary results are reported in two real compounds, the sodium vanadate NaV2O5 and the copper germanate CuGeO3, and in a class of compounds of real materials modeled as dimerized antiferromagnetically coupled spin1/2 chains susceptible to spin1 impurity doping and that include such examples as the strontium cuprate Sr14Cu24O41 and vanadium...
Show moreVarious forms of antiferromagnetic exchange interaction among quantized spins in onedimensional and quasionedimensional lattices are examined. Primary results are reported in two real compounds, the sodium vanadate NaV2O5 and the copper germanate CuGeO3, and in a class of compounds of real materials modeled as dimerized antiferromagnetically coupled spin1/2 chains susceptible to spin1 impurity doping and that include such examples as the strontium cuprate Sr14Cu24O41 and vanadium pyrophosphate (VO)2P2O7. Sodium vanadate, NaV2O5, a quarterfilled twoleg ladder compound that was originally thought to be composed of magnetic legs and nonmagnetic legs was subsequently shown to be a charge ordered system below room temperature. Initial models of the material as isolated antiferromagnetically coupled spin1/2 chains can be mapped to the subsequently resolved magnetic system of the charge ordered state with the spins on molecular orbitals of VOV rungs antiferromagentically coupled between neighboring rungs either on the same ladder or on neighboring ladders. Comparing the model's dynamic structure factor to inelastic neutron scattering data could distinguish between the proposed spin coupling schemes and consequently reveal the details of the interaction between the lattice and the "zigzag" charge density as well as the magnetic stabilization of the low temperature phase. Copper germanate, the first and only known inorganic spinPeierls compound, exhibits a strong temperature dependent exchange coupling pattern among the spin1/2 Cu2+ chains. Above the spinPeierls transition temperature an unmodulated antiferromagnetic nearest neighbor exchange interaction J1 competes with an antiferromagnetic next nearest neighbor interaction J2. The next nearest neighbor exchange represents an effective coupling equivalent to the net effect of all longer range exchange interactions. This frustration to the nearest neighbor spin exchange produces a distinctive magnetic susceptibility χ (T) much different from the BonnerFisher susceptibility of the spin1/2 Heisenberg chain with nearest neighbor antiferromagnetic exchange only. The ratio of the second to first nearest neighbor couplings α = J2/J1 ≈ 0.36 is sufficient to open a spontaneous gap in the spinwave excitation spectrum at low temperatures. Below TSP = 14K, the dynamical structure factor is used to fit the dimerization δ and the exchange interactions J1 and J2 to the inelastic neutron scattering data of CuGeO3 at T = 10K. It is found that both δ and α increase significantly at lower temperatures, relative to the values obtained in the high temperature phase and at the onset of dimeration at 14 K. Static structure factor calculations how Scattering inconsistent with the δâJ1âJ2 model and can be attributed primarily to the phonon degrees of freedom but possibly also to the couplings between chains in the b and a directions of the crystal lattice. Structurally dimerized compounds of antiferromagnetic spin1/2 chains possess dynamic structure factor and magnetic susceptibility features that are very sensitive to doping with magnetic and nonmagnetic impurities. It is shown that the effects of spin1 impurities are very similar to those of nonmagnetic (S = 0) impurities if the coupling between impurity and native spin is about the same magnitude as or larger than between native S = 1/2 spins. The microscopic origins of the similarity can be appreciated with the consideration that neighboring spins to the impurity find it more energetically favorable to couple to the impurity than the other spins of the lattice. Thus the spin1 impurity and its neighboring S = 1/2 spins decouple from the lattice, creating a nonmagnetic break in the chain. The spins that now observe a nonmagnetic cluster on one side can couple to the S = 1/2 spins on the other side with a higher AF correlation than in the pure compound since they do not have to have a ï¬uctuating dimer resonating between two neighbors. Such enhancements to the local correlations can stabilize the global AF order in one dimensional compounds as shown in theoretical and experimental studies of CuGeO3. ED calculations of the dynamic structure factor show that S(q, ω) developes states with ω = 0 in the gap at q = π. Magnetic susceptibilites in the presense of spin1 impurities were obtained for 80 site chains by QMC simulations and for 16 site chains by ED calculations. An impurity concentrationdependent second peak in the low temperature region reveals an increasing second maximum with T as observed in doped copper germanates and suggests that the results of the study are applicable even to phonon mediated dimerization. This is not immediately apparent because spinphonon coupling could distort the dimerization patterns. However, experimental and theoretical results show that elastic coupling between chains can stabilize the dimerization pattern due to the impurities and the results will still apply.
Show less  Date Issued
 2003
 Identifier
 FSU_migr_etd0058
 Format
 Thesis
 Title
 Electron Transport in Strongly Correlated Nanostructures.
 Creator

AlHassanieh, Khaled, Bonesteel, Nicholas, Dalal, Naresh, Piekarewicz, Jorge, Lind, David, Cao, Jianming, Department of Physics, Florida State University
 Abstract/Description

We present the results of our numerical studies on the transport properties of strongly correlated nanostructures, particularly quantum dots and single molecules. The main focus is on correlation, interference and phononic effects. Interesting interferences are observed in multilevel quantum dots, and under the appropriate conditions, a novel ferromagnetic phase is observed in coupled doublelevel quantum dots at quarter filling. Our simulations of experiments involving nonlocal spin control...
Show moreWe present the results of our numerical studies on the transport properties of strongly correlated nanostructures, particularly quantum dots and single molecules. The main focus is on correlation, interference and phononic effects. Interesting interferences are observed in multilevel quantum dots, and under the appropriate conditions, a novel ferromagnetic phase is observed in coupled doublelevel quantum dots at quarter filling. Our simulations of experiments involving nonlocal spin control provide more insight of the experimentally observed results. In the case of single molecules, our study of phonon effects reveals that the centerofmass motion opens a new channel for transport. This channel can interfere destructively with the purely electronic channel leading to a conductance dip. Finally, we propose a new technique to study nanotransport based on the adaptive timedependent densitymatrix renormalization group. The technique is tested for different cases and is very promising particularly in the nonequilibrium case where most other techniques cannot be applied.
Show less  Date Issued
 2007
 Identifier
 FSU_migr_etd0149
 Format
 Thesis
 Title
 Quantum Tunneling and Scattering of a Composite Object.
 Creator

Ahsan, Naureen, Volya, Alexander, Aldrovandi, Ettore, Piekarewicz, Jorge, Crede, Volker, Xiong, Peng, Department of Physics, Florida State University
 Abstract/Description

Reaction physics involving composite objects with internal degrees of freedom is an important subject since it is encountered in the context of nuclear processes like fusion, fission, particle decay, as well as many other branches of science. Quantum tunneling and scattering of a composite object are explored in this work. A few model Hamiltonians are chosen as examples where a twoparticle system interacts, in one dimension, with a target that poses a deltapotential or an infinite wall...
Show moreReaction physics involving composite objects with internal degrees of freedom is an important subject since it is encountered in the context of nuclear processes like fusion, fission, particle decay, as well as many other branches of science. Quantum tunneling and scattering of a composite object are explored in this work. A few model Hamiltonians are chosen as examples where a twoparticle system interacts, in one dimension, with a target that poses a deltapotential or an infinite wall potential. It is assumed that only one of the two components interacts with the target. The study includes the harmonic oscillator and the infinite square well as examples of intrinsic Hamiltonians that do not allow the projectile to break up, and a finite square well and a deltawell as examples of Hamiltonians that do. The Projection Method and the Variable Phase Method are applied with the aim of an exact solution to the relevant scattering problems. These methods are discussed in the context of the pertinent convergence issues related thereto, and of their applicability. Virtual excitations of the projectile into the classically forbidden energydomain are found to play a dominant and nonperturbative role in shaping reaction observables, giving rise to enhanced or reduced tunneling in various situations. Cusps and discontinuities are found to appear in observables as manifestations of unitarity and redistribution of flux at the thresholds. The intrinsic structure gives rise to resonancelike behavior in tunneling probabilities. It is also shown that there is charge asymmetry in the scattering of a composite object, unlike in the case of a structureless particle.
Show less  Date Issued
 2011
 Identifier
 FSU_migr_etd0142
 Format
 Thesis
 Title
 Doping Effects on the Kondo Lattice Materials: FeSi, CeCoin5, and YbInCu4.
 Creator

Yeo, Sunmog, Fisk, Zachary, Dalal, Naresh, Molnar, Stephan von, Bonesteel, Nicholas, Piekarewicz, Jorge, Department of Physics, Florida State University
 Abstract/Description

Three doping studies on Kondo lattices are investigated in this thesis: FeSi1xGex, Ce1xLaxCoIn5, and Yb1xYxInCu4. For FeSi1xGex, we constructed the phase diagram through the analysis of magnetic, thermal and transport measurements on single crystals. The phase diagram shows a firstorder transition from a Kondo insulator (exponentially activated properties) to a ferromagnetic metal at a critical concentration, xc ~ 0:25. The field dependence of the magnetization (M(H)) shows that the...
Show moreThree doping studies on Kondo lattices are investigated in this thesis: FeSi1xGex, Ce1xLaxCoIn5, and Yb1xYxInCu4. For FeSi1xGex, we constructed the phase diagram through the analysis of magnetic, thermal and transport measurements on single crystals. The phase diagram shows a firstorder transition from a Kondo insulator (exponentially activated properties) to a ferromagnetic metal at a critical concentration, xc ~ 0:25. The field dependence of the magnetization (M(H)) shows that the saturation moment of x = 0:27 is 10 times larger than that of x = 0:24. The spin gap of x = 0:24, 167K, is quite close to the transition temperature of x = 0:27, 150K, indicating that the characteristic energies of the two competing phases, i.e. the Curie temperature and the spin gap of the Kondo insulator, are essentially equal at the critical concentration. For x c, spin gap, transport gap and resistivity minimum systematically decrease with increasing x. Saturation moments and specific heat coefficients are almost zero for x c. The temperature dependence of magnetic susceptibility (X(T)) for x = 0:2 shows a broad maximum around 200K, indicating that the broad maximum temperature decreases with x for x c. The variable range hopping analysis suggests the existence of the localized state for this region. For x > x xc, the data break into two distinct regimes: xc» 0:5 and » 0:5 · 1. For xc 0:5, X(T) does not displays a sharp transition at Tc and M(H) increases with increasing fields. The temperature dependence of the resistivity (ρ(T)) shows metallic behavior. However, it does not have any kink at Tc. In contrast, for ~ 0:5 · 1, X(T) displays a sharp transition at Tc and M(H) saturates at H ~ 0:3T. ρ (T) has a kink at Tc. Based on the Kondo insulator picture, we can explain the specific heat coefficient y evolution with x. The transition from a Kondo insulator to a ferromagnetic metal can be explained as the consequence of the changes in hybridization between Fe 3d electrons and Si/Ge p conduction electrons in conjunction with disorder on the Si/Ge ligand site. For Ce1xLaxCoIn5, we studied antiferromagnetic intersite correlations for the Kondo lattice by comparison with data on the single Kondo impurity. All the magnetic susceptibility per mole Ce for H  ab plane and H  c axis collapse onto one curve above 100K in Ce1xLaxCoIn5, indicating the same high T Kondo temperature (~ 35K) for all concentrations. Further, the magnetic part of the resistivity shows the same logT dependence above 50K for all concentrations, again indicating that the high T Kondo temperature is essentially independent of Ce concentration. The magnetic part of the heat capacity for Ce1xLaxCoIn5 alloys has a peak around 70K, suggesting the same crystalline field splittings occurs the alloy series Ce1xLaxCoIn5. Based on these experimental findings, the scaling laws for the susceptibility and the heat capacity reveal that the screening of the magnetic moments in this Kondo lattice involves antiferromagnetic intersite correlations and this intersite correlation has a larger energy scale compared to the Kondo impurity case. In addition, a Fermi liquid ground state appears in the La rich region while the specific heat and inelastic part of ρm show nonFermi liquid behavior for Ce rich region. For Yb1xYxInCu4, measurements using cantilever torque magnetometry discover the new phase above Hv for x = 0 and x = 0:1. With proper scaling of the critical fields and temperatures, data for all alloys collapse onto the same curve, representing a common phase above Hv. The magnetoresistance does not change at the new phase boundary. Due to the crystalline electric field, there is anisotropy of the valence transition in applied magnetic field in different directions. For x = 0:2, the specific heat and the resistance indicate the appearance of a spin glass state below 4K for H > 5T. Since Ytterbium occupies the corners of a tetrahedron in the F43m structure, the spin glass state is not unexpected.
Show less  Date Issued
 2003
 Identifier
 FSU_migr_etd0646
 Format
 Thesis
 Title
 Nuclear Structure of 86Zr and 20O and Beam Pulsing Techniques.
 Creator

Wiedeking, Mathis, Tabor, Samuel L., Logan, Timothy M., Wiedenhöver, Ingo L., Piekarewicz, Jorge, Hagopian, Vasken, Department of Physics, Florida State University
 Abstract/Description

High angular momentum states in 86Zr were populated through the 58Ni(32S,4p) reaction at 135 MeV using the 88Inch Cyclotron at Lawrence Berkeley National Laboratory. Recoiling 86Zr nuclei were stopped in a thick Ta backing. Prompt multiγ coincidences with evaporated charged particles were detected using the full array of Gammasphere and the Microball. Mean lifetimes of 36 levels in 86Zr were measured using the Dopplershift attenuation method. Transition quadrupole moments Qt were found in...
Show moreHigh angular momentum states in 86Zr were populated through the 58Ni(32S,4p) reaction at 135 MeV using the 88Inch Cyclotron at Lawrence Berkeley National Laboratory. Recoiling 86Zr nuclei were stopped in a thick Ta backing. Prompt multiγ coincidences with evaporated charged particles were detected using the full array of Gammasphere and the Microball. Mean lifetimes of 36 levels in 86Zr were measured using the Dopplershift attenuation method. Transition quadrupole moments Qt were found in the range of about 0.3 to 1.5 eb in the positiveparity bands. The negativeparity bands show Qt values from about 0.25 to 1.2 eb In the yrast positiveparity band, a sharp drop in collectivity approaching the 30+ state supports the interpretation of band termination in this configuration. Decreasing Qt values approaching the 24+ and 27 states also provide an indication of terminating structures. Two beam pulsing devices were implemented at the Florida State University Superconducting Linear Accelerator Laboratory. The μs pulsing device consists of parallel plates which deflect the charged ion beam by applying a high voltage. Pulsing electronics controlling the beam deflection and acquisition system with variable time intervals were designed and built. This setup is suitable for lifetime measurements from about a hundred ns up to several ms. The ns pulsing device uses a 48 MHz buncher and two choppers operating at 24 and 6 MHz. This setup is suitable for lifetime measurements in the range of â 1 to 100 ns. An extensive test experiment was performed to verify the accurate operation of these devices by populating known isomeric states with a wide range of lifetimes. Excited states in 20O were populated in the reaction 10Be(14C,α) at Florida State University. Charged particles were detected with a particle telescope consisting of 4 annularly segmented Si surface barrier detectors. The FSU γ detector array was used for γ radiation detection. Five new states were observed below 6 MeV from the αγ and αγγ coincidence data. Shell model calculations suggest that most of the newly observed states are coreexcited 1p1h excitations across the N = Z = 8 shell gap. Comparisons between experimental data and calculations for the neutronrich O and F isotopes imply a steady reduction of the psd shell gap as neutrons are added.
Show less  Date Issued
 2005
 Identifier
 FSU_migr_etd1066
 Format
 Thesis
 Title
 Renormalization Group Study on Coupled Random Antiferromagnetic Spin1/2 Chains.
 Creator

Yusuf, Eddy, Yang, Kun, Dalal, Naresh S., Bonesteel, Nicholas E., Brooks, James S., Piekarewicz, Jorge, Department of Physics, Florida State University
 Abstract/Description

This dissertation is a systematic theoretical effort to investigate the lowenergy properties of random antiferromagnetic quantum spin1/2 systems beyond one dimension. We use the celebrated real space renormalization group (RSRG) technique developed by Dasgupta, Ma, and Hu to understand the static and dynamic properties of random antiferromagnetic spin1/2 ladders and weakly coupled random antiferromagnetic spin1/2 chains. Pure antiferromagnetic spin1/2 ladders are known to be in the spin...
Show moreThis dissertation is a systematic theoretical effort to investigate the lowenergy properties of random antiferromagnetic quantum spin1/2 systems beyond one dimension. We use the celebrated real space renormalization group (RSRG) technique developed by Dasgupta, Ma, and Hu to understand the static and dynamic properties of random antiferromagnetic spin1/2 ladders and weakly coupled random antiferromagnetic spin1/2 chains. Pure antiferromagnetic spin1/2 ladders are known to be in the spin liquid phase with a ¯nite energy gap in the excitation spectrum and a short range spinspin correlation. We are interested in investigating the nature of these systems when disorder, controlled by bond randomness and the presence of impurities, is introduced. Using realspace renormalization group method we are able to find that when disorder comes from bond randomness only, the system flows into a Griffith phase which is characterized by nonuniversal diverging spin susceptibility and shortrange spinspin correlation. When impurities with spin 0 or 1 are introduced into the system, the system flows into a different fixed point which is controlled by large effective spins whose susceptibility is characterized by a universal Curielike 1=T behavior. This conclusion holds for any impurities with integer spin. We also study the lowenergy collective excitations and dynamical response functions of weakly coupled random antiferromagnetic spin1/2 chains at low temperature whose low energy properties are governed by the strongrandomness fixed point. By combining RSRG technique to tackle the intrachain couplings and Random Phase Approximation (RPA) formalism for the interchain couplings, we show that the system supports collective spin wave excitations with linear dispersions and calculate the spin wave velocity in terms of microscopic parameters of the chain. Our result agrees with the measured dispersion for Zndoped CuGeO3 where it shows a linear dispersion along the chain. We predict the spectra weight within RPA which can be qualitatively compared to the scattering intensity in the Inelastic Neutron Scattering experiment.
Show less  Date Issued
 2005
 Identifier
 FSU_migr_etd1151
 Format
 Thesis
 Title
 Physics of Compact Stars.
 Creator

Taruna, Jutri, Piekarewicz, Jorge, Aldrovandi, Ettore, Capstick, Simon, Eugenio, Paul, Reina, Laura, Department of Physics, Florida State University
 Abstract/Description

This thesis starts with a pedagogical introduction to the study of white dwarfs and neutron stars. We will present a stepbystep study of compact stars in hydrostatic equilibrium leading to the equations of stellar structure. Through the use of a simple finitedifference algorithm, solutions to the equations for stellar structure both for white dwarfs and neutron stars are presented. While doing so, we will also introduce the physics of the equation of state and insights on dealing with...
Show moreThis thesis starts with a pedagogical introduction to the study of white dwarfs and neutron stars. We will present a stepbystep study of compact stars in hydrostatic equilibrium leading to the equations of stellar structure. Through the use of a simple finitedifference algorithm, solutions to the equations for stellar structure both for white dwarfs and neutron stars are presented. While doing so, we will also introduce the physics of the equation of state and insights on dealing with units and rescaling the equations. The next project consists of the development of a 'semiclassical' model to describe the equation of state of neutronrich matter in the 'Coulomb frustrated' phase known as nuclear pasta. In recent simulations we have resorted to a classical model that, while simple, captures the essential physics of the nuclear pasta, which consists of the interplay between long range Coulomb repulsion and short range nuclear attraction. However, for the nuclear pasta the de Broglie wavelength is comparable to the average interparticle separation. Therefore, fermionic correlations are expected to become important. In an effort to address this challenge, a fictitious 'Pauli potential' is introduced to mimic the fermionic correlations. In this thesis we will examine two issues. First, we will address some of the inherent difficulties in a widely used version of the Pauli potential. Second, we will refine the potential in a manner consistent with the most basic properties of a degenerate free Fermi gas, such as its momentum distribution and its twobody correlation function. With the newly refined potential, we study various physical observables, such as the twobody correlation function via Metropolis MonteCarlo simulations.
Show less  Date Issued
 2008
 Identifier
 FSU_migr_etd1687
 Format
 Thesis
 Title
 Direct Reactions with Exotic Beams and Polarized Lithium Beams.
 Creator

Roeder, Brian T., Kemper, Kirby, Keel, Brooks, Wiedenhoever, Ingo, Piekarewicz, Jorge, Myers, Edmund, Department of Physics, Florida State University
 Abstract/Description

In the first two chapters of this dissertation, the total cross sections for 38 different reaction products produced in the interaction of 48Ca, 40S and 42S beams at energies around 100 MeV/nucleon with a liquid deuterium target are reported. The cross sections for the 48Ca+d products are compared to those with 48Ca incident on the commonly used fragmentation targets 9Be and 181Ta, and also to global calculations for fragmentation reaction cross sections based on the EPAX parameterization...
Show moreIn the first two chapters of this dissertation, the total cross sections for 38 different reaction products produced in the interaction of 48Ca, 40S and 42S beams at energies around 100 MeV/nucleon with a liquid deuterium target are reported. The cross sections for the 48Ca+d products are compared to those with 48Ca incident on the commonly used fragmentation targets 9Be and 181Ta, and also to global calculations for fragmentation reaction cross sections based on the EPAX parameterization performed with the program LISE. The sizes of the measured reaction cross sections for the deuterium target were comparable to the cross sections measured on the heavier targets indicating that both nucleon addition and removal from a deuterium target can be carried out for comparative "stripping" and "pickup" reaction studies. It was also found that the charge exchange cross sections were large enough so that it should be possible to obtain nuclear structure information from these reactions. Calculations using the JohnsonSoper adiabatic model and Eikonal nucleon knockout theory were performed to study the reaction mechanisms for the "stripping" and "pickup" reactions studied in the experiment. It was found that the magnitude of the cross sections for both the single nucleon "stripping" and single nucleon "pickup" reactions were consistent with the assumption that they proceeded as direct, single step reactions. In the third chapter of this dissertation, the recent upgrade to the Florida State University Optically Pumped Polarized Lithium Ion Source (OPPLIS) is summarized. A new laser system was installed, and the laser optics were modified to increase the laser power available for optically pumping the lithium atomic beam from about 40 mW to nearly 200 mW. This improvement, along with proper alignment of the laser beam divergence to the atomic beam divergence, increased the vector polarization t10 of the beam ontarget from about 40% to about 60%.
Show less  Date Issued
 2006
 Identifier
 FSU_migr_etd1941
 Format
 Thesis
 Title
 Exotic Nuclei and Relativistic MeanField Theory.
 Creator

Rutel, Bonnie Gwen, Piekarewicz, Jorge, Capstick, Simon, Cottle, Paul, Reina, Laura, Kopriva, David A., Department of Physics, Florida State University
 Abstract/Description

A relativistic meanfield model is used to study the groundstate properties of neutronrich nuclei. Nonlinear isoscalarisovector terms, unconstrained by present day phenomenology, are added to the model Lagrangian in order to modify the poorly known density dependence of the symmetry energy. These new terms soften the symmetry energy and reshape the theoretical neutron drip line without compromising the agreement with existing groundstate information. A strong correlation between the...
Show moreA relativistic meanfield model is used to study the groundstate properties of neutronrich nuclei. Nonlinear isoscalarisovector terms, unconstrained by present day phenomenology, are added to the model Lagrangian in order to modify the poorly known density dependence of the symmetry energy. These new terms soften the symmetry energy and reshape the theoretical neutron drip line without compromising the agreement with existing groundstate information. A strong correlation between the neutron radius of Pb208 and the binding energy of valence orbitals is found: the smaller the neutron radius of Pb208, the weaker the binding energy of the last occupied neutron orbital. Thus, models with the softest symmetry energy are the first ones to drip neutrons. Further, in anticipation of the upcoming onepercent measurement of the neutron radius of Pb208 at the Thomas Jefferson Laboratory, a close relationship between the neutron radius of Pb208 and neutron radii of elements of relevance to atomic parityviolating experiments is established. On the basis of relativistic mean field calculations, we demonstrate that the spinorbit splitting of p3/2 and p1/2 neutron orbits depends sensitively on the magnitude of the proton density near the center of the nucleus, and in particular on the occupation of s1/2 proton orbits. We focus on two exotic nuclei, Ar46 and Hg206, in which the presence of a pair of s1/2 proton holes would cause the spinorbit splitting between the p3/2 and p1/2 neutron orbits near the Fermi surface to be much smaller than in the nearby doublymagic nuclei Ca48 and Pb208. We also explore how partial occupancy of the s1/2 proton orbits affects this quenching. We note that these two exotic nuclei depart from the longstanding paradigm of a central potential proportional to the ground state baryon density and a spinorbit potential proportional to the derivative of the central potential.
Show less  Date Issued
 2004
 Identifier
 FSU_migr_etd1956
 Format
 Thesis
 Title
 Thermodynamics of the MagneticFieldInduced "Normal" State in an Underdoped High T[subscript c] Superconductor.
 Creator

Riggs, Scott Chandler, Boebinger, Gregory Scott, Larbalestier, David C., Piekarewicz, Jorge, Bonesteel, Nicholas, Balicas, Luis, Department of Physics, Florida State University
 Abstract/Description

High magnetic fields are used to kill superconductivity and probe what happens to system when it cannot reach the ideal ground state, i.e. what is the normalstate ground state? Early work in HighTc, where the application of magnetic field destroyed the zero resistance state and recovered a resistivity value that connected continuously with the zero field curve, lead people to believe this magneticfieldinducedstate had fully driven the system normal, revealing the true underlying ground...
Show moreHigh magnetic fields are used to kill superconductivity and probe what happens to system when it cannot reach the ideal ground state, i.e. what is the normalstate ground state? Early work in HighTc, where the application of magnetic field destroyed the zero resistance state and recovered a resistivity value that connected continuously with the zero field curve, lead people to believe this magneticfieldinducedstate had fully driven the system normal, revealing the true underlying ground state, without any vestige of superconductivity. Many experiments done in this region of phase space have results interpreted as coming from the low energy ground state excitations. With the emergence of ultraclean crystals in a unique family of hole doped highTc superconductors, YBa2Cu3O7δ, YBCO, a new and highly unexpected phenomena of quantum oscillations were discovered, and they followed the standard LiftshitzKosevich (LK) theory for a normal metal. The results suddenly made the problem of HighTc appear to be analogous to superconductivity in the organics, which is brought about by a wavevector nesting and Fermi surface reconstruction. The only problem, it appeared, that needed to be reconciled was with Angle Resolved PhotoEmission Spectroscopy (ARPES) and Scanning Tunneling Microscopy (STM) data that claimed to see no such Fermi surface, instead only "arcs", a set of disconnected segments in the Brillouin zone which quasiparticle peaks are observed at the Fermi energy, which in a mean field description does not allow for a continuous Fermi surface contour. These two discrepancies led to the "arc vs pocket" debate, which is still unresolved. The other kink in the quantum oscillation armor is that, to this date, quantum oscillations in the holedoped cuprates have only been seen in YBCO, the only cuprate structure to have CuO chains, which conduct and are located in between two CuO2 superconducting planes in the unit cell. In an attempt to reconcile the "arc vs pocket" debate we measure specific heat on an ultraclean detwinned single crystal of underdoped YBCO 6.56 with a Tc = 60 K, up to fields twice irreversibility field, define as the onset of the resistive transition. The zero temperature extrapolation of the electronic contribution to the specific heat, γ, is the total quasiparticle density of states. For a twodimensional system with parabolic energy bands, γ is simply the sum of each pocket multiplied by its effective mass. Therefore, by determining gamma at high fields and using previously determined values for the effective mass from quantum oscillation transport measurements we can simply play a counting game to determine the number of pockets in the Fermi surface. Furthermore, at low fields the response to the specific heat as a function of magnetic field in a dwave superconductor is known to have a √(H) dependence, and we can look for deviations from this√(H), which are expected to happen when the system is no longer in a superconducting state. Results from our specific heat experiment shed new light on the true nature of the magnetic field induced "normal" state, and should force reinterpretation of many experimental findings. The specific heat measurements foremost show a smooth evolution of gamma from low to high magnetic fields which follows a Ac√(H) dependence, with the prefactor, Ac, giving the correct magnitude for the anisotropy of the dwave superconducting gap. This means with the application of magnetic fields strong enough to restore the resistive state, the superconducting gap still exits. Additionally, we see quantum oscillations that follow conventional LK formalism and can determine an effective mass uniquely, where no fitting parameters are required. Interestingly, these oscillations fit on top of the √(H) finding. How can the √(H) and quantum oscillation whose phenomena arise from very different physics be reconciled? Looking at our own zero field γ value of 1.85 mJ mol1K2, which is intrinsic for YBCO, allows the pocket counting game to begin. Coupling bandstructure calculations, angle dependent quantum oscillation measurements, which determine the shape of the pocket, with the zero field γ value leads to the simplest interpretation; quantum oscillatory phenomena is a manifestation of the CuO chain and BaO insulating layer orbital hybridization band and is likely not relevant to high temperature superconductivity.
Show less  Date Issued
 2010
 Identifier
 FSU_migr_etd1859
 Format
 Thesis
 Title
 Molecular Templated Assembly of SingleWalled Carbon Nanotubes and Their Electrical Characterization.
 Creator

Rao, Saleem Ghaffar, Xiong, Peng, Chase, P. Bryant, Brooks, James, Piekarewicz, Jorge, Bonesteel, Nicholas, Department of Physics, Florida State University
 Abstract/Description

We have developed a method for rapid, massivelyparallel assembly and alignment of single walled carbon nanotubes (SWCNT) on a solidstate substrate. The results opened the possibility of production of SWCNTbased integrated circuits. In this strategy called "surfacetemplated assembly", SWCNTs from a solvent suspension are directed toward molecular patterns on the substrate and selfassemble onto specific locations with precise orientations. Since the method does not rely on any external...
Show moreWe have developed a method for rapid, massivelyparallel assembly and alignment of single walled carbon nanotubes (SWCNT) on a solidstate substrate. The results opened the possibility of production of SWCNTbased integrated circuits. In this strategy called "surfacetemplated assembly", SWCNTs from a solvent suspension are directed toward molecular patterns on the substrate and selfassemble onto specific locations with precise orientations. Since the method does not rely on any external forces or slow serial patterning techniques, it can be done in a completely parallel manner and is suitable for highthroughput applications. We have demonstrated the assembly of millions of individual SWCNTs and SWCNTbased circuit structures over ~1cm2 size sample surface in a matter of minutes. The experiments were first carried out on patterned hybrid selfassembled monolayers (SAM) of polar molecules and nonpolar molecules. Polar molecules were patterned with SAM of nonpolar molecules, such as 1octadecanethiol (ODT). The molecular templated substrates were used successfully to assemble SWCNT. Polar molecules with different tail groups, both positive and negative, were shown to be effective, in contrast to the prediction that only molecules with positive tails can be used to align SWCNTs. Furthermore, we observed that the interaction between SWCNTs and metal surfaces also can be used to align SWCNTs using only nonpolar molecular patterns. A series of controlled experiments showed that the number density of aligned SWCNTs depends upon the nature of polar molecules and metal surfaces. We have also assembled SWCNTs on patterns of Au nanoparticles. Au nanoparticle patterns were created on composite SAM templates of nonpolar (ODT) and dithiol (octanedithiol) molecules through selfassembly of Au nanopaticles onto the dithiol region. On such templates, we found very strong adhesion of SWCNTs on Au nanoparticles and no adhesion on the nonpolar regions. We also examined systematically the adhesion of SWCNT on nonpolar molecules with varying coverage of Au. We found no SWCNT attachment when Au coverage is significant but incomplete. Strong adhesion of SWCNT is observed only when the coverage of nonpolar regions by Au is almost complete. These results indicates that nonpolar molecules like ODT play an active role in the alignment of SWCNT on ODT/metal and polar SAMs/ODT hybrid structures. Metal nanoparticle patterns on SAM can also be created via simple metal deposition. With the deposition of a thin metal (Au, Ti, Cr, etc.) film, cluster formation was observed over microscale SAM of nonpolar molecules while for polar molecule patterns of comparable size no cluster formation was observed. Using this surfacetemplated assembly process we have successfully produced field effect transistors (FET) based on SWCNT. SWCNTs were directed to assemble across prepatterned source and drain electrodes (Au or Pd) on a dopedSi/SiO2 substrate. The electrical characteristics of these selfassembled SWCNTFETs are comparable to those fabricated with traditional lithographic methods while the large hystereses observed in the FET action of those devices were significantly reduced. We attribute this to the molecular passivation of the SiO2 surface by octadecyltrichlorosilane (OTS). This observation could have significant implications in exploiting the potential of such devices for chemical and biological sensing.
Show less  Date Issued
 2005
 Identifier
 FSU_migr_etd2119
 Format
 Thesis
 Title
 Phenomenology of Supergravity Models with NonUniversal Scalar Masses.
 Creator

Mustafayev, Azar, Baer, Howard, Aldrovandi, Ettore, Reina, Laura, Wahl, Horst D., Piekarewicz, Jorge, Department of Physics, Florida State University
 Abstract/Description

Supersymmetry (SUSY) is one of the most compelling theoretical extensions of the Standard Model. Many physicists believe that the discovery of SUSY may be imminent and that current and upcoming experiments will finally be able to observe it. Because of the large number of parameters and limited information about physics at very high energy, one should combine all available experimental results with cosmological date in order to determine viable models. One of the major unknowns in SUSY is the...
Show moreSupersymmetry (SUSY) is one of the most compelling theoretical extensions of the Standard Model. Many physicists believe that the discovery of SUSY may be imminent and that current and upcoming experiments will finally be able to observe it. Because of the large number of parameters and limited information about physics at very high energy, one should combine all available experimental results with cosmological date in order to determine viable models. One of the major unknowns in SUSY is the origin and pattern of the supersymmetry breaking scalar masses. For the sake of simplicity, they are usually taken to be universal at the grand unification (GUT) scale. In this study, we discuss theoretical motivations for scalar mass nonuniversality and explore its experimental signatures. We show that the seemingly innocuous deviation from universality in scalar masses can significantly alter our expectations in terms of dark matter as well as (s)particle physics phenomenology. This dissertation is devoted to the analysis of scalar mass nonuniversality in supergravity models and consists of two parts. After a brief review of phenomenology of models with universality, in the first part, we relax universality of scalar mass terms between generations at GUT scale. This should be done with great care  breaking generational universality of the GUTscale soft masses induces flavorviolating processes at the weak scale. We find that recent constraints from b →sγ, (g −2)μ and relic density of neutralino Dark Matter can be simultaneously satisfied if one makes the third generation scalar masses heavier than the degenerate first and second generation scalar masses. This scenario has light sleptons that yield large rates for multilepton processes that, as we have shown in our study, make it testable at the LHC, LC and possibly at the Tevatron. In the second part, we have examined the possibility that the soft SUSY breaking mass parameters in the Higgs sector are unrelated to the matter scalar masses mo. We conducted extensive investigation of one and two parameter models of this type. Previously it was known that making Higgs mass squared parameters independent of mo and positive can lower relic density for almost any mSUGRA point. In this study we have found for the first time the particular correlation of Higgs mass squared parameters with other SUSY parameters and experimental observables in the viable parameter space. For example, we have found that allowing Higgs mass squared parameters to take negative values can decrease the axial Higgs boson mass to the Afunnel (2mZ1 mA) with a neutralino relic density in accord with WMAP results even at low tanβ. This wasn't possible for positive Higgs mass squared parameters. We also study implications of these models for Dark Matter detection experiments and collider searches.
Show less  Date Issued
 2006
 Identifier
 FSU_migr_etd2158
 Format
 Thesis
 Title
 The Development of Femtosecond Electron Diffraction for Direct Measurements of Ultrafast Atomic Motions.
 Creator

Park, Hyuk, Cao, Jianming, Safron, Sanford A., Bonesteel, Nicholas, Piekarewicz, Jorge, Xiong, Peng, Department of Physics, Florida State University
 Abstract/Description

The evolution of material structures is governed by the making and breaking of chemical bonds and the rearrangement of atoms, which occurs on the time scale of an atomic vibrational period, hundreds of femtoseconds. Atomic motion on this time scale ultimately determines the course of phase transitions in solids, the kinetic pathways of chemical reactions, and even the function of biological processes. Direct observation and understanding these ultrafast structural dynamics at the time and...
Show moreThe evolution of material structures is governed by the making and breaking of chemical bonds and the rearrangement of atoms, which occurs on the time scale of an atomic vibrational period, hundreds of femtoseconds. Atomic motion on this time scale ultimately determines the course of phase transitions in solids, the kinetic pathways of chemical reactions, and even the function of biological processes. Direct observation and understanding these ultrafast structural dynamics at the time and length scales of atomic motions represent an important frontier in scientific research and applications. We have developed a femtosecond electron diffraction system (FED) capable of directly measuring the atomic motions in subpicosecond temporal resolution and submilliangstrom spatial resolution. In the path of the development of FED various technical challenges have been overcome and an unprecedented capability has been achieved. These advancements allow us to study a range of ultrafast structural dynamics directly on the fundamental level of atomic motions for the first time. With FED we measured laserinduced ultrafast structural dynamics in a 20nm Al film by taking realtime snapshots of transmission electron patterns. The damped singlemode breathing motion of the Al film along the surface normal was recorded as coherent and inphase oscillations of all the Bragg peak positions. The concurrent lattice heating was measured by tracking the associated Bragg peak intensity attenuation. This acoustic phonon can be well fitted with a classical harmonic oscillator model using a driving force which includes both electronic and lattice contribution. The pressure of the free electrons contributes significantly in driving the coherent acoustic phonons under nonequilibrium conditions when electrons and phonons are not thermalized. In addition, by using a pair of optical excitation pulses and varying their time delay and relative pulse intensities, we demonstrated successful control of coherent lattice motions.
Show less  Date Issued
 2006
 Identifier
 FSU_migr_etd2265
 Format
 Thesis
 Title
 Numerical Studies of Strongly Correlated Electrons in Transition Metal Oxides.
 Creator

Moraghebi, Mohammad, Moreo, Adriana, Safron, Sanford A., Bonesteel, Nicholas E., Piekarewicz, Jorge, Cao, Jianming, Department of Physics, Florida State University
 Abstract/Description

The purpose of this dissertation is to study different properties of the transition metal oxides, especially the highTc superconductors. Applying Monte Carlo methods to a Spin Fermion model, the behavior of the band structure, Fermi surface, pairing correlations, and optical conductivity are studied. The numerical simulations are done at different temperatures, and densities relevant for the cuprates Previous Monte Carlo simulations of this model have shown the existence of charge stripes...
Show moreThe purpose of this dissertation is to study different properties of the transition metal oxides, especially the highTc superconductors. Applying Monte Carlo methods to a Spin Fermion model, the behavior of the band structure, Fermi surface, pairing correlations, and optical conductivity are studied. The numerical simulations are done at different temperatures, and densities relevant for the cuprates Previous Monte Carlo simulations of this model have shown the existence of charge stripes separated by anti ferromagnetic domains upon doping. These results are consistent with neutron scattering experiments. At half ling the ground state of the SpinFermion model is an insulator. The doped holes contribute to the formation of midgap bands by modifying the valence and the conduction band. The ground state appears to change from an insulator to a conductor. In the metallic regime the lower midgap and conduction bands overlap each other giving rise to a pseudogap in the density of states at the chemical potential. This agrees with the results from ARPES experiments. Both midgap and valence bands determine the Fermi surface. The Dwave pairing correlations, for all values of parameters, are stronger than Swave. The Dwave pairing correlations are the strongest in the direction perpendicular to the dynamic stripes which appear in the ground state at some dopings. An optimal doping, where correlations are maximized, is observed close to 25% with an estimated critical temperature Tc = 100 200K in qualitative agreement with highTc cuprates phenomenology. The optical conductivity and Drude weight are studied as a function of electronic density and temperature. As temperature is reduced, spectral weight is transferred from high to low frequencies in agreement with the behavior observed experimentally. Varying the hole density, the Drude weight has a maximum at the optimal doping for the model are stronger. The inverse of the Drude weight, which is roughly proportional to resistivity, decreases linearly with temperature at the optimal doping, and it is abruptly reduced when robust pairing correlations develop upon further reducing the temperature. The general form of the optical conductivity is in good agreement with the experimental results for the cuprates.
Show less  Date Issued
 2003
 Identifier
 FSU_migr_etd2278
 Format
 Thesis
 Title
 Supersymmetry at pp¯, pp and e+e− Colliders in Light of Wmap Measurements of the Dark Matter Density of the Universe.
 Creator

Krupovnickas, Tadas, Baer, Howard, Aldrovandi, Ettore, Reina, Laura, Adams, Todd, Piekarewicz, Jorge, Department of Physics, Florida State University
 Abstract/Description

The Standard Model (SM) describes almost all the particle physics experiments with a high accuracy. However, the SM has a lot of conceptual problems (spontaneous symmetry breaking is introduced by hand, the Higgs boson mass has to be very finely finetuned, there is no explanation for the number of generations or particle quantum numbers, there are at least 19 arbitrary model parameters). Therefore, it is reasonable to search for theories solving some or all of the problems that the SM has....
Show moreThe Standard Model (SM) describes almost all the particle physics experiments with a high accuracy. However, the SM has a lot of conceptual problems (spontaneous symmetry breaking is introduced by hand, the Higgs boson mass has to be very finely finetuned, there is no explanation for the number of generations or particle quantum numbers, there are at least 19 arbitrary model parameters). Therefore, it is reasonable to search for theories solving some or all of the problems that the SM has. One class of such theories is based on an assumption that at some large energy scale Nature chooses the maximal possible spacetime symmetry, called supersymmetry (SUSY). Once the theory is constructed, it has to be tested against the experiment. This dissertation explores various collider signals in the framework of minimal Supergravity model (mSUGRA) and gaugino mediated SUSY breaking model (inoMSB). We calculate whether the signal predicted by these models could be detected at the Fermilab Tevatron and at the CERN LHC hadronic colliders, and also explore the capabilities of a future electronpositron Linear Collider. We show the collider reach contours in the mSUGRA parameter space, combined with constraints from other experiments. We also devise new cuts, optimizing the signal to background ratio in the regions where no such work was previously done.
Show less  Date Issued
 2004
 Identifier
 FSU_migr_etd2897
 Format
 Thesis
 Title
 Transport Properties in Unconventional Superconductors.
 Creator

Cui, Qinghong, Yang, Kun, Dalal, Naresh S., Bonesteel, Nicholas E., Cao, Jianming, Piekarewicz, Jorge, Department of Physics, Florida State University
 Abstract/Description

This dissertation investigates the transport properties of unconventional superconductors which differ from the conventional superconductors on two aspects, one is the pairing symmetry of the order parameter, the other is the net momentum of the Cooper pair. The former ones are discovered in high$T_c$ cuprates, heavyfermion, Sr$_2$RuO$_4$ and so on. The latter ones can be realized by splitting the Fermi surfaces of spinup and down electrons under Zeeman field and are known as the Fulde...
Show moreThis dissertation investigates the transport properties of unconventional superconductors which differ from the conventional superconductors on two aspects, one is the pairing symmetry of the order parameter, the other is the net momentum of the Cooper pair. The former ones are discovered in high$T_c$ cuprates, heavyfermion, Sr$_2$RuO$_4$ and so on. The latter ones can be realized by splitting the Fermi surfaces of spinup and down electrons under Zeeman field and are known as the FuldeFerrellLarkinOvchinnikov (FFLO) states. This work is consisted of two parts. In the first part, we present results of numerical studies of spin quantum Hall transitions in disordered superconductors, in which the pairing order parameter breaks timereversal symmetry. We focus mainly on $p$wave superconductors in which one of the spin components is conserved. The transport properties of the system are studied by numerically diagonalizing pairing Hamiltonians on a lattice, and by calculating the Chern and Thouless numbers of the quasiparticle states. We find that in the presence of disorder, (spin)current carrying states exist only at discrete critical energies in the thermodynamic limit, and the spinquantum Hall transition driven by an external Zeeman field has the same critical behavior as the usual integer quantum Hall transition of noninteracting electrons. These critical energies merge and disappear as disorder strength increases, in a manner similar to those in lattice models for integer quantum Hall transition. The second part is a proposal of identifying the FFLO state based on its transport properties in the normal metal/superconductor junction (NSJ). The FFLO state has received renewed interest recently due to the experimental indication of its presence in CeCoIn$_5$, a quasi 2dimensional (2D) $d$wave superconductor. However direct evidence of the spatial variation of the superconducting order parameter, which is the hallmark of the FFLO state, does not yet exist. In this work we examine the possibility of detecting the phase structure of the order parameter directly using conductance spectroscopy through NSJ, which probes the phase sensitive surface Andreev bound states of $d$wave superconductors. We employ the BlonderTinkhamKlapwijk formalism to calculate the conductance characteristics between a normal metal and a 2D $s$ or $d_{x^2y^2}$wave superconductor in the FuldeFerrell state, for all barrier parameter $z$ from the point contact limit ($z=0$) to the tunneling limit ($z gg 1$). We find that the zerobias conductance peak due to these surface Andreev bound states observed in the uniform $d$wave superconductor is split and shifted in the FuldeFerrell state. We also clarify what weighted bulk density of states is measured by the conductance in the limit of large $z$.
Show less  Date Issued
 2007
 Identifier
 FSU_migr_etd2950
 Format
 Thesis
 Title
 Topological Quantum Compiling.
 Creator

Hormozi, Layla, Bonesteel, Nicholas E., Bowers, Philip L., Piekarewicz, Jorge, Xiong, Peng, Yang, Kun, Department of Physics, Florida State University
 Abstract/Description

A quantum computer must be capable of manipulating quantum information while at the same time protecting it from error and loss of quantum coherence due to interactions with the environment. Topological quantum computation (TQC) offers a particularly elegant way to achieve this. In TQC, quantum information is stored in exotic states of matter which are intrinsically protected from decoherence, and quantum computation is carried out by dragging particlelike excitations (quasiparticles) around...
Show moreA quantum computer must be capable of manipulating quantum information while at the same time protecting it from error and loss of quantum coherence due to interactions with the environment. Topological quantum computation (TQC) offers a particularly elegant way to achieve this. In TQC, quantum information is stored in exotic states of matter which are intrinsically protected from decoherence, and quantum computation is carried out by dragging particlelike excitations (quasiparticles) around one another in two space dimensions. The resulting quasiparticle trajectories define worldlines in threedimensional spacetime, and the corresponding computation depends only on the topology of the braids formed by the worldlines. Quasiparticles that can be used for TQC are expected to exist in a variety of fractional quantum Hall states, among them the socalled Fibonacci anyons. These quasiparticles are conjectured to exist in the = 12/5 fractional quantum Hall state which has been observed in experiments. It has been shown that qubits can be encoded using three or four Fibonacci anyons and singlequbit gates can be carried out by braiding quasiparticles within each qubit. Braids that approximate singlequbit gates can be found through brute force searching and the result can be systematically improved, to any desired accuracy, by applying the Solovay Kitaev algorithm in SU(2). Twoqubit gates are significantly harder to implement, mostly due to the following two reasons. First, the Hilbert space of the quasiparticles forming two qubits is considerably larger than the Hilbert space of the quasiparticles of a single qubit. Therefore, performing a brute force search to find braids that approximate twoqubit gates, as well as the implementation of the SolovayKitaev algorithm for subsequent improvements are prohibitively more difficult. Second, to construct any entangling twoqubit gate, one needs to braid some xvii of the quasiparticles from one qubit around quasiparticles of the other qubit. This process will inevitably lead to leakage errors, i.e. transitions from the qubit space to other available states in the Hilbert space. In this thesis, I will present several efficient methods to construct twoqubit gates using a specific class of quasiparticles. In particular, I show that the problem of finding braids that correspond to twoqubit gates can be reduced to a series of smaller problems which involve braiding only three objects at a time. The required computational power for finding these braids is equivalent to that needed to find singlequbit gates, therefore, these braids can be found with the same high degree of accuracy and efficiency. The end result of this work is an efficient procedure for translating (or "compiling") arbitrary quantum algorithms into specific braiding patterns for Fibonacci anyons, as well as quasiparticles of certain other fractional quantum Hall states that can be used for TQC.
Show less  Date Issued
 2007
 Identifier
 FSU_migr_etd3779
 Format
 Thesis
 Title
 Grid Computing for Physics Environments.
 Creator

Hone, Joshua J., Dennis, Larry, Schwartz, Dan, Blessing, Susan, Piekarewicz, Jorge, Department of Physics, Florida State University
 Abstract/Description

Compute grids for applications have the potential to solve significant issues which contribute to low data processing and publication rates. This potential includes an ability to transparently manage large amounts of data and to greatly enhance project computing resources. This project proposes construction of a structured computing grid from the combination of several opensource Java web application systems, with the main components being the web service server called Axis and the portal...
Show moreCompute grids for applications have the potential to solve significant issues which contribute to low data processing and publication rates. This potential includes an ability to transparently manage large amounts of data and to greatly enhance project computing resources. This project proposes construction of a structured computing grid from the combination of several opensource Java web application systems, with the main components being the web service server called Axis and the portal called Jet speed. This thesis outlines the main motivations, the system design requirements to answer these motivations, the details of the system implementation, the underlying technology, and the first working compute grid application, running at the Hadronic Nuclear Physics cluster to provide stimulation and analysis services to Jefferson Lab (JLAB) Hall B users. This effort works in conjunction with data grid services provided by the Storage Resource Manager which allow access to CLAS data on tape at JLAB. Technical detail on how to install, troubleshoot, upgrade, start up, navigate, and deploy physics applications to the system is also provided.
Show less  Date Issued
 2003
 Identifier
 FSU_migr_etd3799
 Format
 Thesis
 Title
 Charge and Spin Processes in Anisotropic Materials.
 Creator

Jobiliong, Eric, Brooks, James S., Dalal, Naresh, Dobrosavljevic, Vladimir, Xiong, Peng, Piekarewicz, Jorge, Department of Physics, Florida State University
 Abstract/Description

Several materials have been investigated in order to study charge and spin processes in anisotropic materials, particularly in high magnetic fields. The behavior of charge carriers in graphite based material, such as bulk graphite, mesoscopic graphite and graphite intercalated compound is studied. In novel spin systems, a dense Kondo system, CeAgSb2 which has ferro and antiferromagnetic ordering depending on the direction of the magnetic field has been selected, in order to study the...
Show moreSeveral materials have been investigated in order to study charge and spin processes in anisotropic materials, particularly in high magnetic fields. The behavior of charge carriers in graphite based material, such as bulk graphite, mesoscopic graphite and graphite intercalated compound is studied. In novel spin systems, a dense Kondo system, CeAgSb2 which has ferro and antiferromagnetic ordering depending on the direction of the magnetic field has been selected, in order to study the behavior of the spin in this system. Here, I present briefly an explanation of each part of this work. The nature of the magnetic field dependent metalinsulator behavior has been investigated in bulk highly oriented pyrolytic graphite at low temperatures by electronic transport. The metalinsulator behavior has been examined by applying uniaxial stress to our sample up to 8 kbar and found that the temperature dependence of the resistivity for different magnetic fields is the same as that in ambient pressure. The temperature dependence of the resistivity in mesoscopic graphite (called as few layer graphene or FLG) has a strong dependence on the thickness of the sample. The effect of electric field in FLG has been studied in both magnetic fields and zero field. The Shubnikovde Haas (SdH) oscillations frequency increases with absolute value of the gate voltage. I do not observe the field induced charge density wave transition, which is observed in bulk graphite. The intercalated graphite superconductor CaC6 with Tc ~ 11.5 K has been synthesized and characterized with magnetoresistance measurements. By using the McMillan formula, the electronphonon coupling constant is estimated to be Ê = 0.85 which places this material in the intermediatecoupling regime. The angular dependence of the upper critical field parallel and perpendicular to the superconducting planes suggests that this material is a quasi2D superconductor. Of the dense Kondo materials in the class CeTSb2 (where T = Au, Ag, Ni, Cu, or Pd), CeAgSb2 is special due to its complex magnetic ground state, which exhibits both ferro and antiferromagnetic character below an ordering temperature TO ~ 9.8 K. To further elucidate a description this magnetic ground state, I have carried out a systematic study of single crystalline CeAgSb2 by magnetic, electrical magnetotransport, and SdH studies. At zero field the temperature dependent resistivity below TO is most consistent with antiferromagnetic order, based on transport theory which includes magnon scattering.
Show less  Date Issued
 2006
 Identifier
 FSU_migr_etd3657
 Format
 Thesis
 Title
 Understanding Hidden Order in URu₂Si₂.
 Creator

Janik, John A. (John Allan), Wiebe, Christopher R., Dalal, Naresh, Boebinger, Gregory, Schlottmann, Pedro, Piekarewicz, Jorge, Department of Physics, Florida State University
 Abstract/Description

One of the primary goals of modern condensed matter physics is to elucidate the nature of the ground state in various electronic systems. Many correlated electron materials, such as high temperature superconductors,geometrically frustrated oxides,and lowdimensional magnets are still the objects of fruitful study because of the unique properties which arise due to poorly understood manybody effects. Heavy fermion metals  materials which have high effective electron masses due to these...
Show moreOne of the primary goals of modern condensed matter physics is to elucidate the nature of the ground state in various electronic systems. Many correlated electron materials, such as high temperature superconductors,geometrically frustrated oxides,and lowdimensional magnets are still the objects of fruitful study because of the unique properties which arise due to poorly understood manybody effects. Heavy fermion metals  materials which have high effective electron masses due to these effects  represent a class of materials with exotic properties, such as unusual magnetism, unconventional superconductivity, and "hidden order" parameters. The heavy fermion superconductor URu2Si2 has held the attention of physicists for the last two decades due to the presence of a "hidden order" phase below 17.5 K. It is the goal of the present work to solve the puzzle of hidden order in URu2Si2 and identify the true ground state.
Show less  Date Issued
 2008
 Identifier
 FSU_migr_etd3552
 Format
 Thesis
 Title
 Investigation of Spin Transport and Accumulation in Aluminum Gallium Arsenide.
 Creator

Misuraca, Jennifer, Van Molnár, Stephan, Stiegman, Albert, Xiong, Peng, Bonesteel, Nicholas, Piekarewicz, Jorge, Department of Physics, Florida State University
 Abstract/Description

This dissertation describes spin injection, transport, and detection experiments from Fe electrodes into a bulk AlGaAs channel. This semiconducting alloy is one of a class of persistent photoconductors, chosen as the spin transport medium because its carrier density can be tuned in a controlled manner via photoexcitation through the metal to insulator transition (MIT) in situ. This allows one to determine the dependence of spin lifetime on a variety of external parameters including carrier...
Show moreThis dissertation describes spin injection, transport, and detection experiments from Fe electrodes into a bulk AlGaAs channel. This semiconducting alloy is one of a class of persistent photoconductors, chosen as the spin transport medium because its carrier density can be tuned in a controlled manner via photoexcitation through the metal to insulator transition (MIT) in situ. This allows one to determine the dependence of spin lifetime on a variety of external parameters including carrier density, all on one sample. This research represents the first electrical spindependent measurements in this material and describes the dependence of the Hanle signal size and spin lifetime on bias, temperature, and carrier density. The photoexcitation needed to change the carrier density in this material comes from an infrared lightemitting diode (IR LED). The first step of this project was to characterize the new, highly Si doped Al0.3Ga0.7As heterostructures, in order to determine how the illumination of the sample will affect the parameters of the material. To complete this study, Hall crosses were fabricated from the AlGaAs material and the transport properties were measured between 350 mK and 165 K. The resistivity, carrier density, and mobility were determined as a function of temperature for a variety of different illumination times. From this data, the MIT, scattering mechanisms, and the shape of the band tail of the density of states (DOS) were investigated. In fact, this is the first work to electrically probe the DOS in AlGaAs. Once the materials were characterized, they were used to fabricate lateral spin transport devices. Spin transport and accumulation were studied in detail via Hanle effect measurements, which measure the dephasing of electron spins in a perpendicular magnetic field. From these measurements, the spin lifetime of the material can be calculated, and is in the nanosecond range for all measured carrier densities. The spin lifetimes are measured using three distinct measurement configurations which all give consistent results. The dependence of spin lifetime and Hanle signal size are reported as a function of bias, temperature, and carrier density. This is the first spin transport experiment using a persistently photoconductive material as the spin transport channel in order to change the carrier density of the material in situ. The research in this dissertation successfully provides a framework for the continuation of spin injection and detection studies in this and other alloy semiconductors, and provides insight into how the spin lifetime depends on the doping levels in semiconductors.
Show less  Date Issued
 2012
 Identifier
 FSU_migr_etd5406
 Format
 Thesis
 Title
 Deconfinement Transition in Equilibrium Lattice Gauge Theory with Realistic Boundary Conditions.
 Creator

Wu, Hao, Berg, Bernd A., Brüschweiler, Rafael, Adams, Todd, Piekarewicz, Jorge, Reina, Laura, Department of Physics, Florida State University
 Abstract/Description

Heavyion collision experiments carried out at the Brookhaven National Laboratory, or BNL, and at the European Organization for Nuclear Research, or CERN, provide evidence that matter can be driven from a confined, lowtemperature phase into a deconfined high temperature phase of liberated quarks and gluons. Understanding of the deconfinement transition can bring our knowledge of stronglyinteracting matter to a deeper level. Ab initio equilibrium studies of the thermodynamic equation of...
Show moreHeavyion collision experiments carried out at the Brookhaven National Laboratory, or BNL, and at the European Organization for Nuclear Research, or CERN, provide evidence that matter can be driven from a confined, lowtemperature phase into a deconfined high temperature phase of liberated quarks and gluons. Understanding of the deconfinement transition can bring our knowledge of stronglyinteracting matter to a deeper level. Ab initio equilibrium studies of the thermodynamic equation of state in the deconfined phase are possible in the framework of lattice gauge theory. It is often desired in such studies to approach the infinite volume thermodynamic limit. To accomplish it quickly, most studies have implemented lattices with periodic boundary conditions. However, the physical volumes created at the Brookhaven National Laboratory are small and exploratory work for pure SU(3) lattice gauge theory suggests that boundary effects cannot be neglected. In this work we study the SU(3) deconfined equilibrium phase in small volumes with inside and outside temperatures in the SU(3) scaling region, using a lattice geometry of the doublelayered torus. Our results show substantial finite size effects on the deconfining transition temperature under realistic boundary conditions.
Show less  Date Issued
 2012
 Identifier
 FSU_migr_etd5461
 Format
 Thesis
 Title
 Measurement of the Muon Charge Asymmetry in pp → W + X + → μv + X Events Using the DØ.
 Creator

Hoang, Trang Thi Kieu, Blessing, Susan K., Aldrovandi, Ettore, Askew, Andrew, Owens, Joseph, Piekarewicz, Jorge, Department of Physics, Florida State University
 Abstract/Description

This dissertation describes a measurement of the muon charge asymmetry from W&rarr&mu&nu decay using 7.3 fb1 of data collected from April 2002 to July 2010 using the D0 detector at Fermi National Accelerator Laboratory. The measurement for muons with pseudorapidity &eta
Show moreThis dissertation describes a measurement of the muon charge asymmetry from W&rarr&mu&nu decay using 7.3 fb1 of data collected from April 2002 to July 2010 using the D0 detector at Fermi National Accelerator Laboratory. The measurement for muons with pseudorapidity &eta < 2 probes the charge asymmetry for momentum fraction x from 0.005 to 0.3. The charge asymmetry is compared with the theory predictions generated from RESBOS with CTEQ6.6 parton distribution functions, and from POWHEG with CT10 and MSTW2008 PDFs. The results show good agreement with the electron charge asymmetry measurement from D0. So far, our measurement is the most precise lepton charge asymmetry measurement done at the Tevatron.
Show less  Date Issued
 2012
 Identifier
 FSU_migr_etd5363
 Format
 Thesis
 Title
 NexttoLeadingOrder Corrections to Weak Boson Production with a Massive Quark Jet Pair at Hadron Colliders.
 Creator

Febres Cordero, Fernando, Reina, Laura, Aluﬃ, Paolo, Baer, Howard, Prosper, Harrison, Piekarewicz, Jorge, Department of Physics, Florida State University
 Abstract/Description

We present the calculation of NexttoLeadingOrder Quantum Chromo Dynamics corrections for the production of W or Z weak bosons associated with a bottom antibottom quark pair at hadron colliders (ppbar, pp to W/Z bbbar), including the effects of a nonzero bottomquark mass. We find a considerable reduction of the renormalization and factorization scale dependence of our results with respect to LeadingOrder calculations. In particular, we study the impact of the corrections on the total...
Show moreWe present the calculation of NexttoLeadingOrder Quantum Chromo Dynamics corrections for the production of W or Z weak bosons associated with a bottom antibottom quark pair at hadron colliders (ppbar, pp to W/Z bbbar), including the effects of a nonzero bottomquark mass. We find a considerable reduction of the renormalization and factorization scale dependence of our results with respect to LeadingOrder calculations. In particular, we study the impact of the corrections on the total cross section and invariant mass distributions of the bottom antibottom quark pair at the Fermilab Tevatron ppbar collider. We perform a detailed comparison with a calculation that considers massless bottom quarks and find significant deviations in regions of phase space with small invariant mass of the bottom antibottom quark pair. Our results will be relevant to ongoing and future searches at hadron colliders, as the W/Z bbbar production mode is the main background to important signals, such as light Standard Model Higgs boson production or single topquark production.
Show less  Date Issued
 2007
 Identifier
 FSU_migr_etd4486
 Format
 Thesis
 Title
 Constraining Type Ia Supernovae Progenitor Parameters via Light Curves.
 Creator

Sadler, Benjamin, H¨oﬂich, Peter, Chicken, Eric, Gerardy, Chris, Piekarewicz, Jorge, Prosper, Harrison, Department of Physics, Florida State University
 Abstract/Description

I study thermonuclear explosions of White Dwarf (WD) stars, or socalled Type Ia supernovae (SNe Ia). A WD is the final stage of stellar evolution of a star with an initial mass of less than 8 Solar masses, and the thermonuclear explosion occurs either when the WD is in a close binary system where mass overflows from a companion star in a redgiant or asymptoticbranch giant phase, or when two WDs merge. SNe Ia are as bright as their entire host galaxy, which allows their use as longrange...
Show moreI study thermonuclear explosions of White Dwarf (WD) stars, or socalled Type Ia supernovae (SNe Ia). A WD is the final stage of stellar evolution of a star with an initial mass of less than 8 Solar masses, and the thermonuclear explosion occurs either when the WD is in a close binary system where mass overflows from a companion star in a redgiant or asymptoticbranch giant phase, or when two WDs merge. SNe Ia are as bright as their entire host galaxy, which allows their use as longrange cosmic beacons. Although their maximum brightness may vary by a factor of 20, an empirical correlation between their primary parameters of light curve (LC) shape and their intrinsic brightness allows us to account for the majority of this dispersion, with a residual uncertainty of roughly 20%. This calibration has led to their use as standardizable candles, which led to the discovery of the dark energy. Higher precision is needed to determine the nature of the dark energy, however, and to accomplish this we turn to secondary parameters of LC variation. I have devised a general scheme and developed a code to analyze large sets of LC data for these secondary parameter variations which is based on a combination of theoretical model template fitting and Principal Component Analysis. Novel methods for finding statistical trends in sparselysampled and noncoincidental light curve data are explored and utilized. In practice, data sets for different supernovae are inhomogeneous in time, time coverage and accuracy, but I have developed a method to remap these inhomogeneous data sets of large numbers of individual objects to a homogeneous data set centered in time and magnitude space from which we can obtain the external, primary, and secondary LC parameters of individual objects. The set of external parameters of a given SN include the time of its maximum light in various bands, its distance modulus, the extinction along the light path, and redshift corrections (Kcorrections) due to cosmic expansion. I investigate the intrinsic primary parameter variation of SNe Ia via template fitting, and then probe the secondary LC variations using monochromatic differential analysis in the (UBV) bands. We use photometry from 25 SNe Ia which were recently and precisely observed by the Carnegie Supernova Project to analyze the presence of theoretical modelbased differential LC signatures of MainSequence mass variation of the progenitor stars when they formed, central density variation of the WD at the time of the explosion, and metallicity Z variation the in the progenitors. The light curves in the V band are found to provide the highest accuracy in determining the distance modulus, Kcorrections, extinction, mainsequence mass and central density of the WD progenitor, and also the Vband LCs are insensitive to metallicity. Moreover, the Vband appears to be the band which is most stable for differential creation due to the stability of the differentials with respect to uncertainties in the SNe pairs' primary parameters. The Bband's larger Kcorrection uncertainties and dependence on progenitor metallicity and primary parameter uncertainties discourages its use in secondary parameter differential analysis. As with B, the Uband also suffers large uncertainties in extinction and Kcorrections, but this band is a good indicator of metallicity, because the effects of metallicity variation on differential LCs are larger by an order of magnitude than the MainSequence mass and central density effects combined. Our sample includes three SN1991Tlike objects, but we find no evidence of secondary parameter variation among them, and conclude that this class of object may be identified by its primary LC parameter as well as its lack of secondary parameter features. Accounting for these secondary parameters reduces the residuals in the fiducial LC fits from 0.2 magnitude to approximately 0.02 magnitude, a requirement for highprecision cosmology based on SNe Ia. I also reconstruct the distributions of MainSequence mass, central density, and metallicity for the progenitors of the 25 SNe in our sample. I find that most SNe in our sample originate from stars close to the upper limit of the range of possible MainSequence masses, indicating that most SNe Ia explode relatively soon after the progenitor star's formation. However, the reconstructed progenitor mass distribution displays a long tail down to lowermass objects of about 1.5 Solar masses. The central density secondary parameter distribution is much flatter, and shows SNe originate from WD progenitors of a wide range of central densities, from as low as 1.5E9 grams per cubic centimeter, and up to the limit of accretioninduced collapse, suggesting that some potential SNe Ia progenitors become neutron stars instead. Although our sample size is small, all SN1991bglike objects in it come from progenitors with low reconstructed central density and metallicity secondary parameters. Because SN1991bglike objects are only found in local samples and not in highredshift searches, our findings suggest that these progenitor systems are formed at high redshifts but exhibit long delay times before the explosion.
Show less  Date Issued
 2012
 Identifier
 FSU_migr_etd5156
 Format
 Thesis
 Title
 Entanglement Entropy in Ordered and Quantum Critical Systems.
 Creator

Ding, Wenxin, Yang, Kun, Bowers, Phillip, Bonesteel, Nicholas, Piekarewicz, Jorge, Xiong, Peng, Department of Physics, Florida State University
 Abstract/Description

This dissertation investigates the entanglement properties of extended quantum systems which exhibit either longrange order or quantum criticality. While we mainly focus on the von Neumann entanglement entropy, the mutual information is also studied for certain systems when a mixed state is of concern. For extended quantum systems, all the gapped local Hamiltonians, as well as a large number gapless systems, are known to follow the so called "area law", which states that the entanglement...
Show moreThis dissertation investigates the entanglement properties of extended quantum systems which exhibit either longrange order or quantum criticality. While we mainly focus on the von Neumann entanglement entropy, the mutual information is also studied for certain systems when a mixed state is of concern. For extended quantum systems, all the gapped local Hamiltonians, as well as a large number gapless systems, are known to follow the so called "area law", which states that the entanglement entropy is proportional to the surface area of the subsystem. However, violations of the area law, usually in a logarithmic fashion, do exist in various different systems. They are found to be associated with quantum criticality in certain one dimensional systems. For free fermions in higher dimensions, it is found that the area law is enhanced by a logarithmic factor. Besides, such logarithmic terms also appears as subleading corrections to the area law. The central goal of this dissertation is, by studying specific solvable models, to explore and discuss the connections of such logarithmic divergence of entanglement entropy to quantum criticality and longrange order, and the intrinsic relations among such terms in different dimensions, and seek generalization to interacting systems. In the first part, we study two different systems that both exhibit longrange order, namely magnetically ordered Heisenberg spin systems and BoseEinstein condensate systems, and reveal that this logarithmic divergence (violating the area law) is not particular to quantum criticality. They are present in those longrange ordered systems as well. Therefore, caution must be taken when people try to use such divergence to detect and characterize quantum criticality. In second part, we explore the relation between logarithmic divergence in onedimensional fermionic systems and that of free fermions in higher dimensions. We show that both logarithmic factors share the same origin  the singularity at the Fermi points or Fermi surface  via a toy model. Based on the intuition from our toy model, we make use of the tool of multidimensional bosonization to rigorously rederive the entanglement entropy of free fermions in high dimensions in a simpler way. Then by the convenience of the bosonization technique, we take into account the Fermi liquid interactions, and obtain the leading scaling behavior of the entanglement entropy of Fermi liquids.
Show less  Date Issued
 2012
 Identifier
 FSU_migr_etd4801
 Format
 Thesis
 Title
 Applications of Effective Field Theories to the ManyBody Nuclear Problem and Frustrated Spin Chains.
 Creator

Felline, Cosimo, Piekarewicz, Jorge, Krishnamurti, Ruby, Capstick, Simon, Tabor, Samuel, Schlottmann, Pedro, Department of Physics, Florida State University
 Abstract/Description

Modern effectivetheory techniques are applied to the manybody nuclear problem and frustrated quantum spin chains. A novel approach is proposed for the renormalization of nucleonnucleon operators in a manner consistent with the construction of the effective potential. To test this approach a onedimesional, yet realistic, nucleonnucleon potential is introduced. An effective potential is then constructed by tuning its parameters to reproduce the exact effective range expansion and a variety...
Show moreModern effectivetheory techniques are applied to the manybody nuclear problem and frustrated quantum spin chains. A novel approach is proposed for the renormalization of nucleonnucleon operators in a manner consistent with the construction of the effective potential. To test this approach a onedimesional, yet realistic, nucleonnucleon potential is introduced. An effective potential is then constructed by tuning its parameters to reproduce the exact effective range expansion and a variety of bare operators are renormalized in a fashion compatible with this construction. Predictions for the expectation values of these operators in the ground state reproduce the results of the exact theory with remarkable accuracy (at the 0.5% level). We illustrate the main ideas of this work using the elastic form factor of the deuteron as an example. We also apply th COntractor REnormalizator technique to the study of frustrated antiferromagnetic zigzag spin chains with arbitrary halfinteger spin. A basis is employed in which three neighboring spins are coupled to a welldefined value of the total angular momentum. The basis is then truncated to retain only the lowest lying energy states, and the Hamiltonian renormalized to reproduce the lowlying spectrum of the original system. We prove the necessity of retaining two, rather than one, lowest energy eigenstates as frustration is increased. A finite size scaling approach is used to extract ground state energy densities in good agreement with DMRG calculations and spin gaps in qualitative agreement with the disappearance of the Haldane phase around a=0.3. Moreover, we are able to develop a renormalization group equation that predicts accurately the ground state energy density of the chain in the thermodynamic limit.
Show less  Date Issued
 2004
 Identifier
 FSU_migr_etd4481
 Format
 Thesis
 Title
 Angular Momentum Induced Shape Changes in the RareEarth Nuclei ¹⁵²,¹⁵³Gd and ¹⁵⁹,¹⁶⁰Yb.
 Creator

Campbell, David B., Riley, Mark A., Steinbock, Oliver, Weidenhover, Ingo, Coa, Jianming, Piekarewicz, Jorge, Department of Physics, Florida State University
 Abstract/Description

The technique of studying nuclear structure under the rigors of high angular momentum through the examination of γray cascades has recently undergone an explosion in productivity. These advances have been brought on primarily by the development of new detection systems, such as GAMMASPHERE, which are comprised of numerous individual elements. When these Comptonsuppressed Ge detectors are operated in unison, a remarkable ability to distinguish weak and exotic changes in structure emerges....
Show moreThe technique of studying nuclear structure under the rigors of high angular momentum through the examination of γray cascades has recently undergone an explosion in productivity. These advances have been brought on primarily by the development of new detection systems, such as GAMMASPHERE, which are comprised of numerous individual elements. When these Comptonsuppressed Ge detectors are operated in unison, a remarkable ability to distinguish weak and exotic changes in structure emerges. The current generation of spectrometers have allowed dramatic insight into the nucleus and are eclipsed only by the promises of arrays currently on the horizon. The fundamentals of employing γray spectroscopic techniques to examine the fascinating behavior of rapidly rotating nuclei using these arrays will be discussed. The rare earth region of the nuclear landscape is a significant expanse of heavy nuclei with varying degrees of shell occupation. The region has proven to be a rich environment for studying nuclear structure at high spin. For example, superdeformation, identical bands, and backbending were all discovered in this region. This work explores the advances made on four nuclei from this region: 152,153Gd and 159,160Yb. Extensive additions to the previously known structure were made for each nucleus, exposing an unexpected similarity between 152Gd and 154Dy. Long sought after evidence of an angular momentum induced change in nuclear shape was found for each of the nuclei. This shift, from prolate collective rotation at low spin to oblate single particle behavior at high spin, represents a dramatic change in the method employed by the nucleus to generate angular momentum.
Show less  Date Issued
 2004
 Identifier
 FSU_migr_etd4512
 Format
 Thesis
 Title
 Fermi Surface Reconstruction in Chromium at High Pressure and High Magnetic Fields.
 Creator

Stillwell, Ryan L., Tozer, Stanley, Schlottmann, Pedro, Latturner, Susan, Brooks, James, Piekarewicz, Jorge, Department of Physics, Florida State University
 Abstract/Description

Elemental chromium is an itinerant, antiferromagnet with an incommensurate spin and charge density wave structure below 311 kelvin. The Fermi surface in this state is a direct result of the three dimensional nesting of large portions of the paramagnetic Fermi surface seen above 311 K. Due to the large amount of overlap of two of the electron and hole pockets by the spin density wave vector Q, both of these sheets are gapped and have not been resolved in previous experiments. The sheets of the...
Show moreElemental chromium is an itinerant, antiferromagnet with an incommensurate spin and charge density wave structure below 311 kelvin. The Fermi surface in this state is a direct result of the three dimensional nesting of large portions of the paramagnetic Fermi surface seen above 311 K. Due to the large amount of overlap of two of the electron and hole pockets by the spin density wave vector Q, both of these sheets are gapped and have not been resolved in previous experiments. The sheets of the Fermi surface that are not gapped can be configured by overlapping the remaining sheets through integer translations of the nesting vector, ±nQ. This provides a complex spectra of orbits via observation of the Shubnikovde Haas or de Haasvan Alphen effects. Studies have been performed on chromium, via a variety of high pressure techniques, including diamond anvil and piston cylinder pressure cells, and across multiple magnet platforms. Quantum oscillations have revealed a pressureinduced Fermi surface reconstruction at PSF= 0.93 GPa, due to the suppression of the spin flip transition. Changes were observed in the Fermi surface in the low pressure, longitudinally polarized state, and the high pressure, transversely polarized state and were clearly demonstrated in the spectrum at P= 1.47 GPa. Using the LifshitzKosevich formula, which relates quantum oscillation amplitude to electron effective mass, we found a reduction of manybody correlations by a factor of ∼ 5, above PSF. A high field transition was also observed that showed the field induced reorientation of one component of the spin density wave vector at fields ∼ 40 T. Orientation of the spin density wave vector by cooling through the AFM transition had been seen before, but no work on zerofield cooled samples has been reported previously. This work presents details of the low temperature ground state of AFM chromium, for which both the spin flip transition and the AFM Fermi surface have incomplete theoretical formulations. The understanding and knowledge of the mechanism in chromium for quantum interference oscillations, proposed in early experiments specific to two orbits, was expanded to several orbits in the low frequency FFT spectrum and the relationship of those orbits to well established Landau quantization orbits of similar frequencies was also provided.
Show less  Date Issued
 2013
 Identifier
 FSU_migr_etd8645
 Format
 Thesis
 Title
 Bayesian Neural Networks in DataIntensive High Energy Physics Applications.
 Creator

Perry, Michelle, MeyerBaese, Anke, Prosper, Harrison, Piekarewicz, Jorge, Shanbhag, Sachin, Beerli, Peter, Department of Scientific Computing, Florida State University
 Abstract/Description

This dissertation studies a graphical processing unit (GPU) construction of Bayesian neural networks (BNNs) using large training data sets. The goal is to create a program for the mapping of phenomenological Minimal Supersymmetric Standard Model (pMSSM) parameters to their predictions. This would allow for a more robust method of studying the Minimal Supersymmetric Standard Model, which is of much interest at the Large Hadron Collider (LHC) experiment CERN. A systematic study of the speedup...
Show moreThis dissertation studies a graphical processing unit (GPU) construction of Bayesian neural networks (BNNs) using large training data sets. The goal is to create a program for the mapping of phenomenological Minimal Supersymmetric Standard Model (pMSSM) parameters to their predictions. This would allow for a more robust method of studying the Minimal Supersymmetric Standard Model, which is of much interest at the Large Hadron Collider (LHC) experiment CERN. A systematic study of the speedup achieved in the GPU application compared to a Central Processing Unit (CPU) implementation are presented.
Show less  Date Issued
 2014
 Identifier
 FSU_migr_etd8867
 Format
 Thesis
 Title
 NButterflies: Modeling Weak Morphisms of Strict NGroups.
 Creator

Dungan, Gregory John, Aldrovandi, Ettore, Piekarewicz, Jorge, Agashe, Amod, Aluffi, Paolo, Petersen, Kathleen, Department of Mathematics, Florida State University
 Abstract/Description

Butterflies are an algebraic model of the morphisms of the homotopy category of crossed modules and were originally introduced by Behrang Noohi. Crossed complexes are algebraic structures which generalize crossed modules. The following dissertation is concerned with adapting butterflies to the full subcategory of crossed complexes called reduced ncrossed complexes.
 Date Issued
 2014
 Identifier
 FSU_migr_etd8975
 Format
 Thesis
 Title
 Evidence for Single Top Quark Production Using Bayesian Neural Networks.
 Creator

Kau, Daekwang, Prosper, Harrison B., Aldrovandi, Ettore, Adams, Todd, Reina, Laura, Piekarewicz, Jorge, Department of Physics, Florida State University
 Abstract/Description

We present results of a search for single top quark production in pp collisions using a dataset of approximately 1 fb−1 collected with the DØ detector. This analysis considers the muon+jets and electron+jets final states and makes use of Bayesian neural networks to separate the expected signals from backgrounds. The observed excess is associated with a pvalue of 0.081%, assuming the backgroundonly hypothesis, which corresponds to an excess over background of 3.2 standard deviations for a...
Show moreWe present results of a search for single top quark production in pp collisions using a dataset of approximately 1 fb−1 collected with the DØ detector. This analysis considers the muon+jets and electron+jets final states and makes use of Bayesian neural networks to separate the expected signals from backgrounds. The observed excess is associated with a pvalue of 0.081%, assuming the backgroundonly hypothesis, which corresponds to an excess over background of 3.2 standard deviations for a Gaussian density. The pvalue computed using the SM signal cross section of 2.9 pb is 1.6%, corresponding to an expected significance of 2.2 standard deviations. Assuming the observed excess is due to single top production, we measure a single top quark production cross section of _(p¯p ! tb+X, tqb+X) = 4.4±1.5 pb.
Show less  Date Issued
 2007
 Identifier
 FSU_migr_etd3296
 Format
 Thesis
 Title
 A Model for ππ and πη Photoproduction.
 Creator

Kiswandhi, Alvin Stanza, Capstick, Simon, Aldrovandi, Ettore, Piekarewicz, Jorge, Reina, Laura, Eugenio, Paul, Department of Physics, Florida State University
 Abstract/Description

We describe a model of general twototwobody and twotothreebody hadronic reaction based on a phenomenological Lagrangian approach that satisfies twobody unitary and is relativistic. This model is used to study πη photoproduction. Unitarity is ensured by using the LippmannSchwinger equation to iterate the vertices and dress the propagators to all orders, and by including all possible twobody and quasitwobody intermediate channels. We also study different approximations of the...
Show moreWe describe a model of general twototwobody and twotothreebody hadronic reaction based on a phenomenological Lagrangian approach that satisfies twobody unitary and is relativistic. This model is used to study πη photoproduction. Unitarity is ensured by using the LippmannSchwinger equation to iterate the vertices and dress the propagators to all orders, and by including all possible twobody and quasitwobody intermediate channels. We also study different approximations of the intermediate momenta in a diagram. Gauge invariance is used as a criterion to choose the best approximation. This model has been tested by investigating the nonresonant interactions of ππ and πη photoproduction, in which significant effects are observed. A preliminary comparison of our calculation to an existing πη photoproduction study is made, and is shown to produce consistent results.
Show less  Date Issued
 2008
 Identifier
 FSU_migr_etd2826
 Format
 Thesis
 Title
 Entanglement and Bond Fluctuations in Random Singlet Phases.
 Creator

Tran, Huan Doan, Bonesteel, Nicholas E., Safron, Sanford, Dobrosavljevic, Vladimir, Piekarewicz, Jorge, Engel, Lloyd, Department of Physics, Florida State University
 Abstract/Description

The set of valencebond states  states in which localized spin1/2 particles are correlated in singlet pairs said to be connected by valence bonds  provides a useful basis for visualizing singlet ground states of quantum spin systems. For example, the ground state of the uniform onedimensional nearestneighbor spin1/2 antiferromagnetic (AFM) Heisenberg model (the prototypical spinliquid state) can be viewed as a strongly fluctuating liquid of valence bonds with a powerlaw length...
Show moreThe set of valencebond states  states in which localized spin1/2 particles are correlated in singlet pairs said to be connected by valence bonds  provides a useful basis for visualizing singlet ground states of quantum spin systems. For example, the ground state of the uniform onedimensional nearestneighbor spin1/2 antiferromagnetic (AFM) Heisenberg model (the prototypical spinliquid state) can be viewed as a strongly fluctuating liquid of valence bonds with a powerlaw length distribution. This intuitive picture directly reflects the longrange spin correlations in this state, as well as the existence of gapless excitations created by breaking long bonds. Valencebond states also play a key role in describing the physics of random spin1/2 AFM Heisenberg chains. For these systems, it was shown by Fisher, using a real space renormalization group analysis, that on longlength scales the ground state is described by a single valencebond state known as a random singlet state. This single valencebond state should be viewed as a caricature of the true ground state, which will certainly exhibit bond fluctuations on shortlength scales. In valencebond Monte Carlo (VBMC) simulations valencebond states are used to stochastically sample singlet ground states of quantum spin systems. One of the appealing features of VBMC is that if one imagines viewing the sampled valencebond states over many Monte Carlo time steps the resulting ''movie" would correspond closely to the intuitive resonating valence bond picture described above. For random Heisenberg chains (and related models) VBMC should therefore provide a useful method for directly studying the phenomenon of random singlet formation on longlength scales, while at the same time capturing the shortrange fluctuations which will always be present. In this dissertation I present results of VBMC studies for a class of models which include the uniform and random spin1/2 AFM Heisenberg chains, as well as models describing chains of interacting nonAbelian quasiparticles  exotic quasiparticles conjectured to exist in certain fractional quantum Hall states. In addition to numerically computing and analyzing the socalled valencebond entanglement scaling in these models, I introduce a new quantity which I refer to as the valencebond fluctuation (the central new result and the main contribution of this dissertation). It is shown that this quantity, which is easy to compute in valencebond Monte Carlo, provides a direct signature of random singlet phase formation by essentially allowing one to directly ''see" the ''locking" of the ground state into a particular valencebond state on longlength scales. A detailed scaling analysis of this new quantity is then used to extract the dependence of the fluctuation length scale on disorder strength. Where possible, the results are compared to previous numerical and analytic work on the relevant models.
Show less  Date Issued
 2010
 Identifier
 FSU_migr_etd1533
 Format
 Thesis
 Title
 Search for Resonances in the Photoproduction of ProtonAntiproton Pairs.
 Creator

Stokes, Burnham Edward, Eugenio, Paul, Riccardi, Gregory, Adams, Todd, Dennis, Larry, Ostrovidov, Alexander, Piekarewicz, Jorge, Weygand, Dennis, Department of Physics, Florida...
Show moreStokes, Burnham Edward, Eugenio, Paul, Riccardi, Gregory, Adams, Todd, Dennis, Larry, Ostrovidov, Alexander, Piekarewicz, Jorge, Weygand, Dennis, Department of Physics, Florida State University
Show less  Abstract/Description

Results are reported on the reaction gamma p > p p antip with beam energy in the range 4.85.5 GeV. The data were collected at the Thomas Jefferson National Accelerator Facility in CLAS experiment E01017(G6C). The focus of this study is an understanding of the mechanisms of photoproduction of protonantiproton pairs, and to search for intermediate resonances, both narrow and broad, which decay to p antip. The total measured cross section in the photon energy range 4.85.5 GeV is sigma =...
Show moreResults are reported on the reaction gamma p > p p antip with beam energy in the range 4.85.5 GeV. The data were collected at the Thomas Jefferson National Accelerator Facility in CLAS experiment E01017(G6C). The focus of this study is an understanding of the mechanisms of photoproduction of protonantiproton pairs, and to search for intermediate resonances, both narrow and broad, which decay to p antip. The total measured cross section in the photon energy range 4.85.5 GeV is sigma = 33 +/ 2 nb. Measurement of the cross section as a function of energy is provided. An upper limit on the production of a narrow resonance state previously observed with a mass of 2.02 GeV/c^2 is placed at 0.35 nb. No intermediate resonance states were observed. Meson exchange production appears to dominate the production of the protonantiproton pairs. p p antip with beam energy in the range 4.85.5 GeV. The data were collected at the Thomas Jefferson National Accelerator Facility in CLAS experiment E01017(G6C). The focus of this study is an understanding of the mechanisms of photoproduction of protonantiproton pairs, and to search for intermediate resonances, both narrow and broad, which decay to p antip. The total measured cross section in the photon energy range 4.85.5 GeV is sigma = 33 +/ 2 nb. Measurement of the cross section as a function of energy is provided. An upper limit on the production of a narrow resonance state previously observed with a mass of 2.02 GeV/c^2 is placed at 0.35 nb. No intermediate resonance states were observed. Meson exchange production appears to dominate the production of the protonantiproton pairs.
Show less  Date Issued
 2006
 Identifier
 FSU_migr_etd0391
 Format
 Thesis
 Title
 Studies of Weakly Magnetic Systems of Transition Metal Oxides.
 Creator

Zhou, Zhixian, (Deceased), Jack Crow, Schlottmann, Pedro, Dalal, Naresh, Piekarewicz, Jorge, Xiong, Peng, Brooks, James, Department of Physics, Florida State University
 Abstract/Description

LnBaCo2O5.5 (Ln=Gd, Eu) and Sr3Ru2O7 are examples of weakly magnetic systems of 3d and 4d transition metal oxides, respectively. The former is nonmetallic and exhibits magnetic properties of two sublattice magnetic systems with an inplane ferromagnetic interaction and a relatively weak temperature dependent interplane magnetic coupling. The latter is a paramagnetic metal with strongly correlated electrons near a magnetic instability. The magnetization, resistivity and magnetoresistance (MR)...
Show moreLnBaCo2O5.5 (Ln=Gd, Eu) and Sr3Ru2O7 are examples of weakly magnetic systems of 3d and 4d transition metal oxides, respectively. The former is nonmetallic and exhibits magnetic properties of two sublattice magnetic systems with an inplane ferromagnetic interaction and a relatively weak temperature dependent interplane magnetic coupling. The latter is a paramagnetic metal with strongly correlated electrons near a magnetic instability. The magnetization, resistivity and magnetoresistance (MR) of single crystals of GdBaCo2O5.5 and EuBaCo2O5.5 are measured over a wide range of dc magnetic fields (up to 30 T) and temperature. We confirm that GdBaCo2O5.5 and EuBaCo2O5.5 have a metalinsulator transition accompanied by a spinstate transition at TMI » 365 and 335 K, respectively. The data suggest an equal ratio of low spin (S=0) and intermediate spin (S=1) Co3+ ions below TMI, with no indication of additional spin state transitions. The low field magnetization shows a transition to a highly anisotropic ferromagnetic phase, followed by another magnetic transition to an antiferromagnetic phase at a slightly lower temperature. Significant anisotropy between the ab plane and c axis was observed in magnetic and magnetotransport properties for both compounds. For GdBaCo2O5.5, the resistivity and MR data imply a strong correlation between the spinorder and charge carriers. For EuBaCo2O5.5, the magnetic phase diagram is very similar to its Gd counterpart, but the lowT MR with current flow in the ab plane is positive rather than negative as for GdBaCo2O5.5. The magnitude and the hysteresis of the MR for EuBaCo2O5.5 decrease with increasing temperature, and at higher T the MR changes sign and becomes negative. The difference in the behavior of both compounds may arise from a small valence admixture in the nonmagnetic Eu ions, i.e. a valence slightly less than 3+. The specific heat and electrical resistivity of Sr3Ru2O7 single crystals are measured in several magnetic fields applied along the caxis for temperatures below 2 K and at fields up to 17 T. Near the critical metamagnetic field at B1*~7.8 T, the electronic specific heat divided by temperature increases logarithmically as the temperature decreases, over a large range of T, before saturating below a certain T* (which is sample dependent). This crossover from a nonFermi Liquid to a Fermi Liquid state is also observed in the resistivity data near the critical metamagnetic field for I  c and B  c. At the lowest temperatures, a Schottkylike upturn with decreasing temperature is observed. The coefficient of the Schottky anomaly exhibits a field dependence similar to that of g, implying an influence by the electrons near the Fermi surface on the Schottky level splitting.
Show less  Date Issued
 2004
 Identifier
 FSU_migr_etd0521
 Format
 Thesis
 Title
 Statics and Dynamics of Halide SubMonolayer Electrosorption on Silver: Computer Simulations with Comparison to Experiments.
 Creator

Abou Hamad, Ibrahim, Rikvold, Per Arne, Schlenoﬀ, Joseph B., Piekarewicz, Jorge, Zhou, HuanXiang, Hirst, Linda, Department of Physics, Florida State University
 Abstract/Description

This dissertation investigates equilibrium and dynamical properties of submonolayer chemical adsorption of Br and Cl on singlecrystal Ag(100) electrodes. Computational methods, such as Monte Carlo simulations with Firstorder Reversal Curve analysis, are used along with experimental data. Monte Carlo simulations of a twodimensional latticegas approximation for the adlayer are used to explore equilibrium properties of the system. Lateral interaction energies between adsorbates, as well...
Show moreThis dissertation investigates equilibrium and dynamical properties of submonolayer chemical adsorption of Br and Cl on singlecrystal Ag(100) electrodes. Computational methods, such as Monte Carlo simulations with Firstorder Reversal Curve analysis, are used along with experimental data. Monte Carlo simulations of a twodimensional latticegas approximation for the adlayer are used to explore equilibrium properties of the system. Lateral interaction energies between adsorbates, as well other system parameters like the electrosorption valency, are determined by fitting simulations to experimental chronocoulometry isotherms. While neither the electrosorption valency nor the lateral interactions show any dependence on the adsorbate coverage for the Br/Ag(100) system, a model in which both are coverage dependent is required to adequately describe the Cl/Ag(100) system. A selfconsistent, entirely electrostatic picture of the lateral interactions with coverage dependence is developed, and a relationship between the lateral interactions and the electrosorption valency is investigated for Cl on Ag(100). The adsorbates form a disordered adlayer at low electrochemical potentials. At a more positive electrochemical potential the adlayer undergoes a disorderorder phase transition to an ordered c(2x2) phase. This phase transition produces a peak in the current density observed in cyclicvoltammetry experiments. Kinetic Monte Carlo studies of the latticegas model are used to simulate cyclicvoltammetry experiments. The scanrate dependence of the separation between positive and negativegoing peaks in cyclicvoltammetry simulations are compared to experimental peak separations. This dynamics study identifies the inverse Monte Carlo attempt frequency with a physical timescale. Although kinetic Monte Carlo simulations can provide longtime simulations of the dynamics of physical and chemical systems, this identification is not yet possible in general. To further investigate the dynamics, Firstorder Reversal Curve (FORC) analysisa method that was recently developed and used for magnetic systemsis applied to simulations of electrochemical submonolayer adsorption in systems with first and secondorder phase transitions. Not only does this method highlight differences between the two kinds of phase transitions, but it can also be used to recover the equilibrium behavior for systems with a secondorder phase transition and slow equilibration from dynamic reversal curves.
Show less  Date Issued
 2006
 Identifier
 FSU_migr_etd0103
 Format
 Thesis
 Title
 High Frequency Probes of Superconductivity and Magnetism in Anisotropic Materials in Very High Magnetic Field.
 Creator

Altarawneh, Moaz, Brooks, James, Dalal, Naresh, Mielke, Charles H., Piekarewicz, Jorge, Schlottmann, Pedro, Winkle, David Van, Department of Physics, Florida State University
 Abstract/Description

In this dissertation, I present a study of a wide range of organic and inorganic materials using radio frequency (rf) measurement methods. The organic samples under study were λ(BETS )2 GaCl4 and λ(BETS )2 FeCl4 . In the λ(BETS )2 GaCl4 , the HT superconductivity phase diagram was studied using the tunnel diode oscillator (TDO) method and compared with simultaneous four terminals resistivity measurements. These simultaneous measurements show signs of paraconductivity in this material....
Show moreIn this dissertation, I present a study of a wide range of organic and inorganic materials using radio frequency (rf) measurement methods. The organic samples under study were λ(BETS )2 GaCl4 and λ(BETS )2 FeCl4 . In the λ(BETS )2 GaCl4 , the HT superconductivity phase diagram was studied using the tunnel diode oscillator (TDO) method and compared with simultaneous four terminals resistivity measurements. These simultaneous measurements show signs of paraconductivity in this material. The same method was used to study the λ( BETS )2 FeCl4 sample which is a field induced superconductor (FISC). The inorganic materials that I have studied include Ba 0.55K0.45Fe2 As2 and USb2 . In Ba0.55K0.45Fe 2As2 (which belongs to the recently discovered Pnictide superconductors family), I have studied the HT phase diagram for magnetic fields applied parallel and perpendicular to the crystallographic caxis up to 65 tesla and in temperature as low as 4 K . Ba0.55K0.45 Fe2As2 was studied by a new rf technique that I have developed recently (PDOâ¡Proximity Detector Oscillator). The rf measurements of Ba0.55 K0.45Fe2 As2 from my work support the prediction of an unconventional multigap superconductivity in this material. In the USb 2 sample, a Fermi surfaces measurement was performed by the TDO rf probe and by a torque magnetometer for comparison purposes in high magnetic fields up to 65 tesla and in temperatures above 0.5 K . I found that both the rf and the torque measurements reveal a cylindrical Fermi surface with approximately the same effective mass. However, the rf and the torque measurements reveal some differences in the frequencies obtained from the FFT obtained for each method. In this dissertation, most of the measurements were performed using rf probes like the TDO or the PDO. The PDO method has successfully replaced the TDO method to perform rf measurements in all different kinds of magnets (dc and pulsed).
Show less  Date Issued
 2009
 Identifier
 FSU_migr_etd0186
 Format
 Thesis
 Title
 Study of Magnetic Materials for Biomedical and Other Applications.
 Creator

Ahmad, Shahid Nisar, Shaheen, Shahid A., Strouse, Geoﬀery F., Winkle, David Van, Lind, David, Bonesteel, Nicholas, Piekarewicz, Jorge, Department of Physics, Florida State...
Show moreAhmad, Shahid Nisar, Shaheen, Shahid A., Strouse, Geoﬀery F., Winkle, David Van, Lind, David, Bonesteel, Nicholas, Piekarewicz, Jorge, Department of Physics, Florida State University
Show less  Abstract/Description

We have studied different aspects of magnetic materials in bulk, nanoparticles, and thinfilm form with emphasis on their use in biomedical and technological applications. In this work: 1. We have synthesized several new Gd based compounds and alloys and have optimized their magnetic properties for the selfcontrolled hyperthermia applications. The self controlled hyperthermia is a new noninvasive technique to employ heat treatment to cure cancerous cells without overheating the normal cells....
Show moreWe have studied different aspects of magnetic materials in bulk, nanoparticles, and thinfilm form with emphasis on their use in biomedical and technological applications. In this work: 1. We have synthesized several new Gd based compounds and alloys and have optimized their magnetic properties for the selfcontrolled hyperthermia applications. The self controlled hyperthermia is a new noninvasive technique to employ heat treatment to cure cancerous cells without overheating the normal cells. The need for developing such materials was dictated by the lack of existing magnetic materials with magnetic ordering temperatures in the temperature range of (4045)0C, which is the critical operating temperature range for the hyperthermia applications. 2. We have produced gold coated FeAu nanoparticles which are biocompatible and can easily be functionalized through gold surface for various technological applications, besides hyperthermia applications. Contrary to the previous reports of time dependent degradation of magnetic properties of the FeAu nanoparticles, our gold coated nanoparticles are quite robust and their magnetic properties remain unchanged under the ambient conditions. We have made a comprehensive study of the FeAu nanoparticles, and have observed that superparamgnetic FeAu nanoparticles can be produced with variable Fe content up to 30 at.% and the particle size remains nearly uniform (~ 5 nm). When subjected to annealing at elevated temperatures, the magnetic core in the FeAu nanoparticles undergoes various interesting changes and blocking temperature and magnetization increase when nanoparticles are annealed at elevated temperatures. The observation of the Verwey transition at ~ 125K in the magnetization versus temperature data for the samples annealed at 4500C and above indicates the formation of Fe3O4. The absence of any oxide peaks in the asformed sample and presence of oxide peaks in the samples annealed at 4500C and above in the xray diffraction and xray photoemission data, as well as in the magnetic data, support the model that FeAu alloy core is protected by the Au shell in the asformed state. Annealing at higher temperatures leads to the segregation of Fe and Au, and oxidation of Fe occurs when Au shell is punctured at the elevated temperatures. Also, we have studied the behavior of the asformed and annealed FeAu nanoparticles in the a.c. field upto a frequency of 1 MHz and have demonstrated their suitability for hyperthermia applications. 3. We have investigated the metalorganic interface for its impact on the magnetic properties by sputtering permalloy (Ni79Fe21) on the self assembled monolayers of polar [16mercaptohexadecanoic acid (MHA)] and non polar [1Octadecanethiol (ODT)] organic molecules. It has been observed that permalloy forms films exhibiting ferromagnetic properties for the 4 nm and higher thicknesses on the polar MHA molecules which offer better adhesion to permalloy, on the other hand, it forms scattered superparamgnetic clusters on the ODT molecules which offer poor adhesion. The systematic study of the deposition of permalloy with thickness varying from 2 nm to 70 nm on the selfassembled monolayes of MHA and ODT reveals that the effect of the underlaying organic surfaces decreases as the deposition thickness increases and inplane oriented magnetic thinfilms are produced for 12 nm thickness on both type of surfaces. The squareness of the magnetic hysteresis loop indicates that the best inplane oriented films are produced for the 20 nm thickness, and further increase in the thickness leads to randomization of the orientation of the deposited material on both type of surfaces. We also demonstrated that by sputtering permalloy on the prefabricated templates containing MHA and ODT patterns, small scale (micron size) templates can be made with magnetic and nonmagnetic patterns. The dippen approach may be used to extend the pattering to submicron and nanoscale level.
Show less  Date Issued
 2009
 Identifier
 FSU_migr_etd0124
 Format
 Thesis
 Title
 Relativistic Mean Field Models for Finite Nuclei and Neutron Stars.
 Creator

Chen, WeiChia, Piekarewicz, Jorge, Kopriva, David A., Volya, Alexander, Credé, Volker, Bonesteel, N. E., Florida State University, College of Arts and Sciences, Department of...
Show moreChen, WeiChia, Piekarewicz, Jorge, Kopriva, David A., Volya, Alexander, Credé, Volker, Bonesteel, N. E., Florida State University, College of Arts and Sciences, Department of Physics
Show less  Abstract/Description

In this dissertation we have created theoretical models for finite nuclei, nuclear matter, and neutron stars within the framework of relativistic mean field (RMF) theory, and we have used these models to investigate the elusive isovector sector and related physics, in particular, the neutronskin thickness of heavy nuclei, the nuclear symmetry energy, and the properties of neutron stars. To build RMF models that incorporate collective excitations in finite nuclei in addition to their ground...
Show moreIn this dissertation we have created theoretical models for finite nuclei, nuclear matter, and neutron stars within the framework of relativistic mean field (RMF) theory, and we have used these models to investigate the elusive isovector sector and related physics, in particular, the neutronskin thickness of heavy nuclei, the nuclear symmetry energy, and the properties of neutron stars. To build RMF models that incorporate collective excitations in finite nuclei in addition to their groundstate properties, we have extended the nonrelativistic sum rule approach to the relativistic domain. This allows an efficient estimate of giant monopole energies. Moreover, we have combined an exact shellmodellike approach with the meanfield calculation to describe pairing correlations in openshell nuclei. All the ingredients were then put together to establish the calibration scheme. We have also extended the transformation between model parameters and pseudo data of nuclear matter within the RMF context. Performing calibration in this pseudo data space can not only facilitate the searching algorithm but also make the pseudo data genuine model predictions. This calibration scheme is also supplemented by a covariance analysis enabling us to extract the information content of a model, including theoretical uncertainties and correlation coefficients. A series of RMF models subject to the same isoscalar constraints but one differing isovector assumption were then created using this calibration scheme. By comparing their predictions of the nuclear matter equation of state to both experimental and theoretical constraints, we found that a small neutron skin of about 0.16 fm in Pb208 is favored, indicating that the symmetry energy should be soft. To obtain stronger evidence, we proceeded to examine the evolution of the isotopic chains in both oxygen and calcium. Again, it was found that the model with such small neutron skin and soft symmetry energy can best describe both isotopic chains, and the resultant values of the neutronskin thickness and the symmetry energy are consistent with most current constraints. Finally, we addressed the recent tension between dense matter theory and the observation of neutron stars with rather small stellar radii. By employing Lindblom's algorithm, we were able to derive the underlying equation of state for assumed massradius relations having the "common radius" feature followed by recent analyses. We found that, in order to support twosolarmass neutron stars, the typical stellar radii must be greater than 10.7 km—barely compatible with recent analyses—to prevent the underlying equation of state from violating causality.
Show less  Date Issued
 2015
 Identifier
 FSU_2015fall_Chen_fsu_0071E_12869
 Format
 Thesis
 Title
 NonAbelian Quantum Error Correction.
 Creator

Feng, Weibo, Bonesteel, N. E., Bowers, Philip L., Piekarewicz, Jorge, Yang, Kun, Xiong, Peng, Florida State University, College of Arts and Sciences, Department of Physics
 Abstract/Description

A quantum computer is a proposed device which would be capable of initializing, coherently manipulating, and measuring quantum states with sufficient accuracy to carry out new kinds of computations. In the standard scenario, a quantum computer is built out of quantum bits, or qubits, twolevel quantum systems which replace the ordinary classical bits of a classical computer. Quantum computation is then carried out by applying quantum gates, the quantum equivalent of Boolean logic gates, to...
Show moreA quantum computer is a proposed device which would be capable of initializing, coherently manipulating, and measuring quantum states with sufficient accuracy to carry out new kinds of computations. In the standard scenario, a quantum computer is built out of quantum bits, or qubits, twolevel quantum systems which replace the ordinary classical bits of a classical computer. Quantum computation is then carried out by applying quantum gates, the quantum equivalent of Boolean logic gates, to these qubits. The most fundamental barrier to building a quantum computer is the inevitable errors which occur when carrying out quantum gates and the loss of quantum coherence of the qubits due to their coupling to the environment (decoherence). Remarkably, it has been shown that in a quantum computer such errors and decoherence can be actively fought using what is known as quantum error correction. A closely related proposal for fighting errors and decoherence in a quantum computer is to build the computer out of socalled topologically ordered states of matter. These are states of matter which allow for the storage and manipulation of quantum states with a built in protection from error and decoherence. The excitations of these states are nonAbelian anyons, particlelike excitations which satisfy nonAbelian statistics, meaning that when two excitations are interchanged the result is not the usual +1 and 1 associated with identical Bosons or Fermions, but rather a unitary operation which acts on a multidimensional Hilbert space. It is therefore possible to envision computing with these anyons by braiding their worldlines in 2+1dimensional spacetime. In this Dissertation we present explicit procedures for a scheme which lives at the intersection of these two approaches. In this scheme we envision a functioning "conventional" quantum computer consisting of an array of qubits and the ability to carry out quantum gates on these qubits. We then give explicit quantum circuits (sequences of quantum gates) which can be used to create and maintain a topologically ordered state with nonAbelian anyon excitations using the "conventional" qubits of the computer. Our circuits perform measurements on these qubits which detect "errors" corresponding to deviations from the topologically ordered ground state of interest. We also give circuits which can be used to move these errors and eventually fuse them with other errors to eliminate them.
Show less  Date Issued
 2015
 Identifier
 FSU_2015fall_Feng_fsu_0071E_12902
 Format
 Thesis
 Title
 Electronic Tuning in the Hidden Order Compound URu2Si2 through Si → P Substitution.
 Creator

Gallagher, Andrew, Baumbach, Ryan Eagle, Hill, Stephen (Professor of Physics), Siegrist, Theo, Boebinger, Gregory S. (Gregory Scott), Piekarewicz, Jorge, Florida State...
Show moreGallagher, Andrew, Baumbach, Ryan Eagle, Hill, Stephen (Professor of Physics), Siegrist, Theo, Boebinger, Gregory S. (Gregory Scott), Piekarewicz, Jorge, Florida State University, College of Arts and Sciences, Department of Physics
Show less  Abstract/Description

Crystalline materials that include 4f and 5felectron elements frequently exhibit a variety of intriguing phenomena including spin and charge orderings, spin and valence fluctuations, heavy fermion behavior, breakdown of Fermi liquid behavior, and unconventional superconductivity. [5, 6, 7, 8, 9, 10, 11, 12, 13] Amongst such materials, the Kondo lattice system URu2Si2 stands out as being particularly unusual. [14, 15, 16] While at high temperature it exhibits behavior that is typical for an...
Show moreCrystalline materials that include 4f and 5felectron elements frequently exhibit a variety of intriguing phenomena including spin and charge orderings, spin and valence fluctuations, heavy fermion behavior, breakdown of Fermi liquid behavior, and unconventional superconductivity. [5, 6, 7, 8, 9, 10, 11, 12, 13] Amongst such materials, the Kondo lattice system URu2Si2 stands out as being particularly unusual. [14, 15, 16] While at high temperature it exhibits behavior that is typical for an felectron lattice immersed in a sea of conduction electrons, at T0 = 17:5 K there is a second order phase transition that is followed by unconventional superconductivity near Tc 1:5 K. [15] Despite three decades of work, the order parameter for the transition at T0 remains unknown and hence, it has been named "hidden order". There have been a multitude of experimental attempts to unravel hidden order, mainly through tuning of the electronic state via pressure, applied magnetic field, and chemical substitution. [17, 18] While these strategies reveal interesting phase diagrams, a longstanding challenge is that any such approach explores the phase space along an unknown vector: i.e., many different factors are affected. To address this issue, we developed a new organizational map for the Ubased ThCr2Si2type compounds that are related to URu2Si2 and thus guided, we explored a new chemical tuning axis: Si > P. Our studies were enabled by the development of a new molten metal crystal growth method for URu2Si2 which produces high quality single crystals and allows us to introduce high vapor pressure elements, such as phosphorous. [19, 20] Si > P tuning reveals that while the high temperature Kondo lattice behavior is robust, the low temperature phenomena are remarkably sensitive to electronic tuning. [21, 22] In the URu2Si2xPx phase diagram we find that while hidden order is monotonically suppressed and destroyed for x < 0.035, the superconducting strength evolves nonmonotonically with a maximum near x = 0.01 and that superconductivity is destroyed near x = 0.028. For 0.03 < x < 0.26 there is a region with Kondo coherence but no ordered state. Antiferromagnetism abruptly appears for x = 0.26. This phase diagram differs significantly from those produced by most other tuning strategies in URu2Si2, including applied pressure, and isoelectronic chemical substitution (i.e. Ru > Fe and Os), where hidden order and magnetism share a common phase boundary. [2, 23, 24] We discuss implications for understanding hidden order, its relationship to magnetism, and prospects for uncovering novel sibling electronic states.
Show less  Date Issued
 2017
 Identifier
 FSU_SUMMER2017_Gallagher_fsu_0071E_13976
 Format
 Thesis
 Title
 Mott Transition in Strongly Correlated Materials: ManyBody Methods and Realistic Materials Simulations.
 Creator

Lee, TsungHan, Dobrosavljević, Vladimir, Dalal, Naresh S., Manousakis, Efstratios, Balicas, Luis, Piekarewicz, Jorge, Florida State University, College of Arts and Sciences,...
Show moreLee, TsungHan, Dobrosavljević, Vladimir, Dalal, Naresh S., Manousakis, Efstratios, Balicas, Luis, Piekarewicz, Jorge, Florida State University, College of Arts and Sciences, Department of Physics
Show less  Abstract/Description

Strongly correlated materials are a class of materials that cannot be properly described by the Density Functional Theory (DFT), which is a singleparticle approximation to the original manybody electronic Hamiltonian. These systems contain d or f orbital electrons, i.e., transition metals, actinides, and lanthanides compounds, for which the electronelectron interaction (correlation) effects are too strong to be described by the singleparticle 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 singleparticle approximation to the original manybody electronic Hamiltonian. These systems contain d or f orbital electrons, i.e., transition metals, actinides, and lanthanides compounds, for which the electronelectron interaction (correlation) effects are too strong to be described by the singleparticle approximation of DFT. Therefore, complementary manybody methods have been developed, at the model Hamiltonians level, to describe these strong correlation effects. Dynamical Mean Field Theory (DMFT) and Rotationally Invariant SlaveBoson (RISB) approaches are two successful methods that can capture the correlation effects for a broad interaction strength. However, these manybody 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 metalMott 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 insulatinglike behavior in resistivity while carrying a weak metallic character in its electronic structure. Second, we improved DMFT to describe a Mott insulator containing spinpropagating and chargeless fermionic excitations, spinons. We found the spinon Fermiliquid, in the Mott insulating phase, is immiscible to the electron Fermiliquid, in the metallic phase, due to the strong scattering between spinons in a metal. Third, we proposed a new approach within the slaveboson (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 slaveboson 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 AmO chemical bonding in the CsAm(CrO_4)_2 crystal. Our results indicate the AmO 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 metalMott insulator coexistence regime, the metaltoMottinsulator transition with spinons excitation in the Mottinsulating 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.
Show less  Date Issued
 2017
 Identifier
 FSU_SUMMER2017_Lee_fsu_0071E_13983
 Format
 Thesis