Search results

Title: Multiband Models for Colossal Magnetoresistance Materials and Diluted Magnetic Semiconductors.
Creator: Popescu, Florentin, Bonesteel, Professor N., Dalal, Professor N., Xiong, Professor P., Piekarewicz, Professor J., Chiorescu, Professor I., Department of Physics, Florida State...
Show morePopescu, Florentin, Bonesteel, Professor N., Dalal, Professor N., Xiong, Professor P., Piekarewicz, Professor J., Chiorescu, Professor I., Department of Physics, Florida State University
Show less
Abstract/Description: Several multiband models for Colossal Manetoresistance Materials and Diluted Magnetic Semiconductors are investigated within Dynamical Mean-Field Theory. The theoretical analysis of such models uses extensively the parametrization method for the bare Green's function to study the critical transition temperatures in a wide range of model's parameters; hoping amplitudes, couplings, and carrier concentrations. For both classes of materials, it is found within a two-band model that the transition...
Show moreSeveral multiband models for Colossal Manetoresistance Materials and Diluted Magnetic Semiconductors are investigated within Dynamical Mean-Field Theory. The theoretical analysis of such models uses extensively the parametrization method for the bare Green's function to study the critical transition temperatures in a wide range of model's parameters; hoping amplitudes, couplings, and carrier concentrations. For both classes of materials, it is found within a two-band model that the transition temperature can be twice larger than the one predicted by the one band models and that its maximum is reached at a twice larger carrier concentration. It is also revealed that the off-diagonal hoppings, when considered, lead to a substantial boost of the ferromagnetic transition temperature. By accounting for the attractive Coulomb potential by acceptors in diluted magnetic semiconductors, the impurity to valence band crossover is studied as a function of doping and the critical values of doping, at which the crossover occurs, are estimated for various diluted magnetic semiconductors.
Show less
Date Issued: 2007
Identifier: FSU_migr_etd-0478
Format: Thesis

Title: First Measurement of Top Quark Pair Production Cross-Section in Muon Plus Hadronic Tau Final States.
Creator: Sumowidagdo, Suharyo, Adams, Todd, Aldrovandi, Ettore, Wahl, Horst, Reina, Laura, Capstick, Simon, Department of Physics, Florida State University
Abstract/Description: This dissertation presents the first measurement of top quark pair production cross-section in events containing a muon and a tau lepton. The measurement was done with 1 fb−1 of data collected during April 2002 through February 2006 using the DØ detector at the Tevatron proton-antiproton collider, located at Fermi National Accelerator Laboratory (Fermilab), Batavia, Illinois. Events containing one isolated muon, one tau which decays hadronically, missing transverse energy, and two or more...
Show moreThis dissertation presents the first measurement of top quark pair production cross-section in events containing a muon and a tau lepton. The measurement was done with 1 fb−1 of data collected during April 2002 through February 2006 using the DØ detector at the Tevatron proton-antiproton collider, located at Fermi National Accelerator Laboratory (Fermilab), Batavia, Illinois. Events containing one isolated muon, one tau which decays hadronically, missing transverse energy, and two or more jets (at least one of which must be tagged as a heavy flavor jet) were selected.Twenty-nine candidate events were observed with an expected background of 9.16 events. The top quark pair production cross-section is measured to beσ (t¯t) = 8.0+2.8 −2.4 (stat)+1.8−1.7 (syst) ± 0.5 (lumi) pb.Assuming a top quark pair production cross-section of 6.77 pb for Monte Carlo signal top events without a real tau, the measured σ × BR isσ (t¯t) × BR(t¯t μ +τ + 2ν + 2b) = 0.18+0.13−0.11 (stat)+0.09−0.09 (syst) ± 0.01 (lumi) pb.
Show less
Date Issued: 2008
Identifier: FSU_migr_etd-0407
Format: Thesis

Title: SO(10) Supersymmetric Grand Unified Theories: from Cosmology to Colliders.
Creator: Summy, Heaya Ann, Baer, Howard, Sussman, Mark, Reina, Laura, Wahl, Horst, Manousakis, Efstratios, Department of Physics, Florida State University
Abstract/Description: Simple SUSY GUT models based on the gauge group SO(10) require t-b-t Yukawa coupling unification, in addition to gauge coupling and matter unification. The Yukawa coupling unification places a severe constraint on the expected spectrum of superpartners, with scalar masses ~ 10 TeV while gaugino masses are quite light. For Yukawa-unified models with μ > 0, the spectrum is characterized by three mass scales: i). first and second generation scalars in the multi-TeV range, ii). third generation...
Show moreSimple SUSY GUT models based on the gauge group SO(10) require t-b-t Yukawa coupling unification, in addition to gauge coupling and matter unification. The Yukawa coupling unification places a severe constraint on the expected spectrum of superpartners, with scalar masses ~ 10 TeV while gaugino masses are quite light. For Yukawa-unified models with μ > 0, the spectrum is characterized by three mass scales: i). first and second generation scalars in the multi-TeV range, ii). third generation scalars, μ and mA in the few-TeV range and iii). gluinos in the ~ 350−500 GeV range with chargino masses around 100−160 GeV. In such a scenario, gluino pair production should occur at large rates at the CERN LHC, followed by gluino three-body decays into neutralinos or charginos. Discovery of Yukawa-unified SUSY at the LHC should hence be possible with only 1 fb−1 of integrated luminosity, by tagging multi-jet events with 2–3 isolated leptons, without relying on missing ET . A characteristic dilepton mass edge should easily be apparent above Standard Model background. Combining dileptons with b-jets, along with the gluino pair production cross section information, should allow for gluino and neutralino mass reconstruction. A secondary corroborative signal should be visible at higher integrated luminosity in the X1±1X20 → 3l channel, and should exhibit the same dilepton mass edge as in the gluino cascade decay signal. A problem generic to all supergravity models comes from overproduction of gravitinos in the early universe: if gravitinos are unstable, then their late decays may destroy the predictions of Big Bang nucleosynthesis. We also present a Yukawa-unified SO(10) SUSY GUT scenario which avoids the gravitino problem, gives rise to the correct matter-antimatter asymmetry via non-thermal leptogenesis, and is consistent with the WMAP-measured abundance of cold dark matter due to the presence of an axino LSP. To maintain a consistent cosmology for Yukawa-unified SUSY models, we require a re-heat temperature TR ~ 106−107 GeV, an axino mass around 0.1−10 MeV, and a Peccei-Quinn breaking scale fa ~ 1012 GeV.
Show less
Date Issued: 2008
Identifier: FSU_migr_etd-0405
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 in-depth 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_etd-0406
Format: Thesis

Title: Search for Resonances in the Photoproduction of Proton-Antiproton 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 anti-p with beam energy in the range 4.8-5.5 GeV. The data were collected at the Thomas Jefferson National Accelerator Facility in CLAS experiment E01-017(G6C). The focus of this study is an understanding of the mechanisms of photoproduction of proton-antiproton pairs, and to search for intermediate resonances, both narrow and broad, which decay to p anti-p. The total measured cross section in the photon energy range 4.8-5.5 GeV is sigma =...
Show moreResults are reported on the reaction gamma p -> p p anti-p with beam energy in the range 4.8-5.5 GeV. The data were collected at the Thomas Jefferson National Accelerator Facility in CLAS experiment E01-017(G6C). The focus of this study is an understanding of the mechanisms of photoproduction of proton-antiproton pairs, and to search for intermediate resonances, both narrow and broad, which decay to p anti-p. The total measured cross section in the photon energy range 4.8-5.5 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 proton-antiproton pairs. p p anti-p with beam energy in the range 4.8-5.5 GeV. The data were collected at the Thomas Jefferson National Accelerator Facility in CLAS experiment E01-017(G6C). The focus of this study is an understanding of the mechanisms of photoproduction of proton-antiproton pairs, and to search for intermediate resonances, both narrow and broad, which decay to p anti-p. The total measured cross section in the photon energy range 4.8-5.5 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 proton-antiproton pairs.
Show less
Date Issued: 2006
Identifier: FSU_migr_etd-0391
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 in-plane ferromagnetic interaction and a relatively weak temperature dependent inter-plane 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 in-plane ferromagnetic interaction and a relatively weak temperature dependent inter-plane 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 metal-insulator transition accompanied by a spin-state 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 a-b 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 spin-order and charge carriers. For EuBaCo2O5.5, the magnetic phase diagram is very similar to its Gd counterpart, but the low-T 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 c-axis 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 non-Fermi 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 Schottky-like 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_etd-0521
Format: Thesis

Title: Measurements of the Differential Cross Sections for the Inclusive Production of a Photon and Heavy Flavor Jet.
Creator: Duggan, Daniel J., Wahl, Horst, Schatschneider, Chris, Adams, Todd, III, Joseph Owens, Manousakis, Efstratios, Department of Physics, Florida State University
Abstract/Description: This thesis presents the first measurement of the differential production cross section of a heavy flavor (bottom or charm) jet and direct photon at the Fermilab Tevatron. These measurements were performed using data recorded with the D0 detector from proton-antiproton collisions at a center of mass energy of sqrt(s) = 1.96 TeV. These results probe a kinematic range for the photon transverse momentum of 30 to 150 GeV and photon rapidity |y|
Date Issued: 2009
Identifier: FSU_migr_etd-0649
Format: Thesis

Title: Structural Behavior of 157,158,159Dy in the I=30−50L Spin Regime and the High-Spin 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 rare-earth nuclei with mass extit{A}$sim$158. Significant extensions to the high-spin excitation spectrum of the $N$=91, 92, 93 isotopes $^{157,158,159}$Dy have been achieved using the high-efficiency $gamma$-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 rare-earth nuclei with mass extit{A}$sim$158. Significant extensions to the high-spin excitation spectrum of the $N$=91, 92, 93 isotopes $^{157,158,159}$Dy have been achieved using the high-efficiency $gamma$-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 high-spin 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 Nilsson-Strutinsky calculations without pairing have been performed for detailed comparisons with the very high-spin states observed in $^{157}$Dy. Results on $^{157,158,159}$Dy have been published in extit{Phys. Rev. C.} Moreover, the angular-momentum induced transition from a deformed state of collective rotation to a non-collective 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 Nilsson-Strutinsky calculations suggest that these states arise from weakly collective configurations that break the $Z$=64 semi-magic core. Additionally, a new frontier of discrete-line $gamma$-ray spectroscopy at ultra-high spin has been opened in the rare-earth 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 band-terminating states in these nuclei near extit{I}$sim$45$hbar$. Cranked Nilsson-Strutinsky calculations suggest that these structures arise from well-deformed triaxial configurations that lie in a valley of favored shell energy, which also includes the well-known triaxial strongly deformed bands in $^{161-167}$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 odd-odd nucleus $^{158}$Tb. Unfortunately, no new significant results on the latter were obtained except for the tentative assignment of a new, strongly-coupled, rotational structure.}
Show less
Date Issued: 2006
Identifier: FSU_migr_etd-0687
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 (spin-dependent) 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 (spin-dependent) 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 spin-dependent 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 thiol-gold 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 thiol-gold 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 I-V 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 two-component model based on a picture of intrinsic (non-chemical) 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_etd-0540
Format: Thesis

Title: Physical Properties of Novel Magnetic Heterostructures.
Creator: Dzero, Maxim O., Gor'kov, L. P., Dalal, N., Dobrosavljević, V., Piekarewicz, J., Department of Physics, Florida State University
Abstract/Description: There is an ongoing interest in studying the novel magnetic systems, such as magnetoresistance structures (GMR), magnetic dilute semiconductors and various magnetic nanostructures. In the first part of my dissertation I present the results of our work concerning the possibility of using ferromagnetic metallic manganites as basic elements for various GMR heterostructures. I start by studying the phase diagram of maganites using the general band approach. As it turns out, the basic properties...
Show moreThere is an ongoing interest in studying the novel magnetic systems, such as magnetoresistance structures (GMR), magnetic dilute semiconductors and various magnetic nanostructures. In the first part of my dissertation I present the results of our work concerning the possibility of using ferromagnetic metallic manganites as basic elements for various GMR heterostructures. I start by studying the phase diagram of maganites using the general band approach. As it turns out, the basic properties of the maganites to a large extent are determined by cooperative Jahn-Teller effects and the Hund's rule coupling. The transition from insulating antiferromagnetic to metallic ferromagnet state at critical doping concentration Xcr is treated by means of the percolation theory.
Show less
Date Issued: 2003
Identifier: FSU_migr_etd-0612
Format: Thesis

Title: A Precision Measurement of the 1S2S 1S0 – 1S2P 3P1 Interval in Helium-like Silicon Using Fast-Beam Laser Spectroscopy.
Creator: Devore, Thomas Robert, Myers, Edmund, Safron, Sanford, Adams, Todd, Capstick, Simon, Rogachev, Grigory, Department of Physics, Florida State University
Abstract/Description: In this dissertation, we present a precision measurement of the 1s2s 1S0 – 1s2p 3P1 intercombination interval in the moderate-Z helium-like ion, 28Si12+, using a fast-beam laser resonance technique. This experiment is a second-generation measurement designed to surpass the precision of the previous measurement of Redshaw et al. (Phys. Rev. Lett., 88 (2002) 023002), using an improved laser setup designed to cancel the Doppler shift. This was accomplished by incorporating a counter-propagating...
Show moreIn this dissertation, we present a precision measurement of the 1s2s 1S0 – 1s2p 3P1 intercombination interval in the moderate-Z helium-like ion, 28Si12+, using a fast-beam laser resonance technique. This experiment is a second-generation measurement designed to surpass the precision of the previous measurement of Redshaw et al. (Phys. Rev. Lett., 88 (2002) 023002), using an improved laser setup designed to cancel the Doppler shift. This was accomplished by incorporating a counter-propagating laser at 1,450 nm into the previous setup that used a co-propagating laser at 1,319 nm to induce the same transition. Our final result for this energy interval is 7,230.585(6) cm–1 with an overall precision of 0.8 parts-per-million (ppm). This result represents a 30-fold improvement over the previous measurement, and tests QED contributions at the level of 13 ppm. The two-electron atom/ion is a fundamental atomic system, and continues to be the subject of major theoretical work today. Hence, our precise measurement provides a clear test of modern theory, including higher-ordered QED effects.
Show less
Date Issued: 2008
Identifier: FSU_migr_etd-0757
Format: Thesis

Title: Nuclear Magnetic Resonance Studies of Phase Separation in Two Systems: La1-xSrxCoO3 and La2-xSrxCuO4.
Creator: Smith, Robert Steven, Boebinger, Gregory, Dalal, Naresh, Brooks, James, Dobrosavljevic, Vladimir, Tabor, Samuel, Reyes, Arneil, Department of Physics, Florida State University
Abstract/Description: Nuclear magnetic resonance measurements are reported for two systems: La1-xSrxCoO3 and La2−xSrxCuO4. The local nature of NMR finds local order at temperatures well above the bulk phase transitions of these compounds. This demonstrates the important role of fluctuations in strongly correlated systems. La1−xSrxCoO3: Nanoscale inhomogeneity in La1−xSrxCoO3) has been investigated in single crystal samples for 0.05≤x≤0.30 using 139La and 59Co NMR to probe local magnetization. Ferromagnetism is...
Show moreNuclear magnetic resonance measurements are reported for two systems: La1-xSrxCoO3 and La2−xSrxCuO4. The local nature of NMR finds local order at temperatures well above the bulk phase transitions of these compounds. This demonstrates the important role of fluctuations in strongly correlated systems. La1−xSrxCoO3: Nanoscale inhomogeneity in La1−xSrxCoO3) has been investigated in single crystal samples for 0.05≤x≤0.30 using 139La and 59Co NMR to probe local magnetization. Ferromagnetism is only exhibited above the metal-to-insulator (MIT) critical concentration, xC. However, over the entire doping range, the single crystals exhibit an unusually broad and asymmetric distribution of hyperfine fields, evidencing (local) magnetic cluster formation that persists to temperatures as high as 200 K, well above the glass transition reported from bulk magnetization. Above xC the asymmetry decreases rapidly with increasing doping as magnetic clusters overlap to give rise to long-range ferromagnetism. The key features of the spectra are reproduced by a simple model in which Sr dopants trigger magnetic cluster formation. Relaxation measurements at various locations in the magnetic clusters show the correlation times of the fluctuating hyperfine fields becomes very slow on the edges of a magnetic cluster due to large amounts of disorder. Below the MIT the system is made of two regions, a) the very weakly magnetic regions outside a cluster where Co3+ ions undergo spin-state transitions nearly identical to the parent compound, and b) the disorder spin-glass regions made up of the magnetic clusters. The clusters grow slowly with doping and see only a slowly changing density of states until they begin to merge at x=0.10 where they grow rapidly and the carrier density drops. La2−xSrxCuO4: At intense magnetic fields (30T)17O NMR exhibits two distinct signatures for planar oxygen sites instead of the singular site expected from the identical lattice symmetry at oxygen sites in the copper-oxygen plane for underdoped, orthorhombic La2−xSrxCuO4. Analysis of Knight shift, linewidth, quadrupolar splitting and spectral asymmetry indicates that roughly 75% of the planar oxygens evidence antiferromagnetically-correlated nearest neighbor Cu moments at temperatures below ∼30 K, consistent with previous reports. A second planar oxygen site first observed in this study shows that there are mobile holes on roughly 25% of the planar oxygen sites that (a) suppress magnetism for all T<300K and>(b) show a Knight shift that drops to zero below ∼60 K, evidencing pair formation at a temperature well above the superconducting transition temperature (∼4 K at 30 T) and more than twice the superconducting transition temperature at zero magnetic field.
Show less
Date Issued: 2010
Identifier: FSU_migr_etd-0365
Format: Thesis

Title: Numerical Study of Spin-Fermion 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, Spin-Fermion (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 III-V semiconductors is proposed. This model includes the appropriate lattice geometry, as well as, magnetic, spin-orbit, and Coulomb interactions and contains no free parameters. Its study using state-of-the-art numerical techniques provides results in...
Show moreIn this dissertation, Spin-Fermion (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 III-V semiconductors is proposed. This model includes the appropriate lattice geometry, as well as, magnetic, spin-orbit, and Coulomb interactions and contains no free parameters. Its study using state-of-the-art numerical techniques provides results in excellent agreement with experimental data for Mn doped GaAs. For the first time, Curie-Weiss 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 spin-fermion model. Both diagonal and off-diagonal electron-phonon interactions are considered. While diagonal terms tend to stabilize ordered structures such as stripes, the off-diagonal terms introduce disorder making this structures more dynamical. Our results indicate that phonons play a role in the stabilization of stripe-like states.
Show less
Date Issued: 2007
Identifier: FSU_migr_etd-0668
Format: Thesis

Title: Symmetry and Control in Spin-Based Quantum Computing.
Creator: Stepanenko, Dimitrije, Bonesteel, Nicholas E., Mio, Washington, Dobrosavljevi´c, Vladimir, Molnar, Stephan von, Riley, Mark, Department of Physics, Florida State University
Abstract/Description: A promising proposal for quantum computation, due to Loss and DiVincenzo, is based on using electron spins in quantum dots as qubits - two-level systems which are the quantum analogues of classical bits. Two-qubit operations (quantum gates) are then carried out by switching on and off the exchange interaction between neighboring spins (i.e. "pulsing" the interaction). This thesis presents a study of the effect of anisotropic corrections to the exchange interaction due to spin-orbit coupling...
Show moreA promising proposal for quantum computation, due to Loss and DiVincenzo, is based on using electron spins in quantum dots as qubits - two-level systems which are the quantum analogues of classical bits. Two-qubit operations (quantum gates) are then carried out by switching on and off the exchange interaction between neighboring spins (i.e. "pulsing" the interaction). This thesis presents a study of the effect of anisotropic corrections to the exchange interaction due to spin-orbit coupling on this scheme. It is shown that time-symmetric pulsing automatically eliminates some undesirable terms in the resulting quantum gates, and well-chosen pulse shapes can produce an effectively isotropic exchange gate which can be used for universal quantum computation. Deviations from perfect time-symmetric pulsing are then studied in the context of a microscopic model of GaAs quantum dots. A new proposal for universal quantum computation which uses control of anisotropic corrections is then presented. In this proposal, the number of pulses required to carry out quantum gates scales as the inverse of a dimensionless measure of the degree of control. The size of this dimensionless figure-of-merit" depends on (i) variation of anisotropy with interdot distance, and (ii) restrictions on the pulse duration due to decoherence for slow pulses and nonadiabatic transitions for fast pulses. Taking these constraints into account, the figure-of-merit is estimated for GaAs quantum dots and shown to be large enough to be useful forquantum computation.
Show less
Date Issued: 2005
Identifier: FSU_migr_etd-0378
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_etd-0027
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 fine-tuning 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 wino-like LSP.
Show less
Date Issued: 2004
Identifier: FSU_migr_etd-0037
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 one-dimensional and quasi-one-dimensional 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 spin-1/2 chains susceptible to spin-1 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 one-dimensional and quasi-one-dimensional 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 spin-1/2 chains susceptible to spin-1 impurity doping and that include such examples as the strontium cuprate Sr14Cu24O41 and vanadium pyrophosphate (VO)2P2O7. Sodium vanadate, NaV2O5, a quarter-filled two-leg 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 spin-1/2 chains can be mapped to the subsequently resolved magnetic system of the charge ordered state with the spins on molecular orbitals of V-O-V 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 "zig-zag" charge density as well as the magnetic stabilization of the low temperature phase. Copper germanate, the first and only known inorganic spin-Peierls compound, exhibits a strong temperature dependent exchange coupling pattern among the spin-1/2 Cu2+ chains. Above the spin-Peierls 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 Bonner-Fisher susceptibility of the spin-1/2 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 spin-wave 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 spin-1/2 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 spin-1 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 spin-1 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 spin-1 impurities were obtained for 80 site chains by QMC simulations and for 16 site chains by ED calculations. An impurity concentration-dependent 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 spin-phonon 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_etd-0058
Format: Thesis

Title: Statics and Dynamics of Halide Sub-Monolayer Electrosorption on Silver: Computer Simulations with Comparison to Experiments.
Creator: Abou Hamad, Ibrahim, Rikvold, Per Arne, Schlenoﬀ, Joseph B., Piekarewicz, Jorge, Zhou, Huan-Xiang, 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 single-crystal Ag(100) electrodes. Computational methods, such as Monte Carlo simulations with First-order Reversal Curve analysis, are used along with experimental data. Monte Carlo simulations of a two-dimensional lattice-gas 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 single-crystal Ag(100) electrodes. Computational methods, such as Monte Carlo simulations with First-order Reversal Curve analysis, are used along with experimental data. Monte Carlo simulations of a two-dimensional lattice-gas 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 self-consistent, 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 disorder-order phase transition to an ordered c(2x2) phase. This phase transition produces a peak in the current density observed in cyclic-voltammetry experiments. Kinetic Monte Carlo studies of the lattice-gas model are used to simulate cyclic-voltammetry experiments. The scan-rate dependence of the separation between positive- and negative-going peaks in cyclic-voltammetry 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 long-time simulations of the dynamics of physical and chemical systems, this identification is not yet possible in general. To further investigate the dynamics, First-order Reversal Curve (FORC) analysis---a method that was recently developed and used for magnetic systems---is applied to simulations of electrochemical submonolayer adsorption in systems with first- and second-order 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 second-order phase transition and slow equilibration from dynamic reversal curves.
Show less
Date Issued: 2006
Identifier: FSU_migr_etd-0103
Format: Thesis

Title: The Emergence of Collective Phenomena in Systems with Random Interactions.
Creator: Abramkina, Volha, Volya, Alexander, Okten, Giray, Capstick, Simon, Rogachev, Grigory, Rikvold, Per Arne, Department of Physics, Florida State University
Abstract/Description: Emergent phenomena are one of the most profound topics in modern science, addressing the ways that collectivities and complex patterns appear due to multiplicity of components and simple interactions. Ensembles of random Hamiltonians allow one to explore emergent phenomena in a statistical way. In this work we adopt a shell model approach with a two-body interaction Hamiltonian. The sets of the two-body interaction strengths are selected at random, resulting in the two-body random ensemble ...
Show moreEmergent phenomena are one of the most profound topics in modern science, addressing the ways that collectivities and complex patterns appear due to multiplicity of components and simple interactions. Ensembles of random Hamiltonians allow one to explore emergent phenomena in a statistical way. In this work we adopt a shell model approach with a two-body interaction Hamiltonian. The sets of the two-body interaction strengths are selected at random, resulting in the two-body random ensemble (TBRE). Symmetries such as angular momentum, isospin, and parity entangled with complex many-body dynamics result in surprising order discovered in the spectrum of low-lying excitations. The statistical patterns exhibited in the TBRE are remarkably similar to those observed in real nuclei. Signs of almost every collective feature seen in nuclei, namely, pairing superconductivity, deformation, and vibration, have been observed in random ensembles. In what follows a systematic investigation of nuclear shape collectivities in random ensembles is conducted. The development of the mean field, its geometry, multipole collectivities and their dependence on the underlying two-body interaction are explored. Apart from the role of static symmetries such as SU(2) angular momentum and isospin groups, the emergence of dynamical symmetries including the seniority SU(2), rotational symmetry, as well as the Elliot SU(3) is shown to be an important precursor for the existence of geometric collectivities.
Show less
Date Issued: 2011
Identifier: FSU_migr_etd-0104
Format: Thesis

Title: High-Fold Angular Correlation Studies and the Terminating 12+ State of 24Mg.
Creator: Diffenderfer, Eric S., Wiedenhover, Ingo, Steinbock, Oliver, Bonesteel, Nicholas E., Tabor, Samuel L., Volya, Alexander S., Department of Physics, Florida State University
Abstract/Description: A new angular correlation analysis technique for assigning spins to alpha-unbound states of nuclei that feed alpha-unbound states of other nuclei is described. A kinematically complete experiment was performed to study the reaction ¹²C(¹⁶O, alpha)²⁴Mg*, populating alpha-unbound states of ²⁴Mg that decay to alpha-unbound states of ²⁰Ne, where all final state particles were detected. The new analysis technique was used to unambiguously identify the first Ipi = 12+ state of ²⁴Mg at 26.3 MeV. The...
Show moreA new angular correlation analysis technique for assigning spins to alpha-unbound states of nuclei that feed alpha-unbound states of other nuclei is described. A kinematically complete experiment was performed to study the reaction ¹²C(¹⁶O, alpha)²⁴Mg*, populating alpha-unbound states of ²⁴Mg that decay to alpha-unbound states of ²⁰Ne, where all final state particles were detected. The new analysis technique was used to unambiguously identify the first Ipi = 12+ state of ²⁴Mg at 26.3 MeV. The new 12+ state is discussed in the context of the collective and shell models.
Show less
Date Issued: 2007
Identifier: FSU_migr_etd-0081
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 H-T 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 para-conductivity 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 H-T 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 para-conductivity 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 H-T phase diagram for magnetic fields applied parallel and perpendicular to the crystallographic c-axis 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_etd-0186
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 self-controlled hyperthermia applications. The self controlled hyperthermia is a new non-invasive 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 self-controlled hyperthermia applications. The self controlled hyperthermia is a new non-invasive 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 (40-45)0C, which is the critical operating temperature range for the hyperthermia applications. 2. We have produced gold coated Fe-Au 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 Fe-Au 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 Fe-Au nanoparticles, and have observed that superparamgnetic Fe-Au 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 Fe-Au 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 as-formed sample and presence of oxide peaks in the samples annealed at 4500C and above in the x-ray diffraction and x-ray photoemission data, as well as in the magnetic data, support the model that Fe-Au alloy core is protected by the Au shell in the as-formed 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 as-formed and annealed Fe-Au 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 metal-organic interface for its impact on the magnetic properties by sputtering permalloy (Ni79Fe21) on the self assembled monolayers of polar [16-mercaptohexadecanoic acid (MHA)] and non polar [1-Octadecanethiol (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 self-assembled 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 non-magnetic patterns. The dip-pen approach may be used to extend the pattering to submicron and nanoscale level.
Show less
Date Issued: 2009
Identifier: FSU_migr_etd-0124
Format: Thesis

Title: High-Spin Nuclear Structure of 168,170Ta and Triaxial Strongly Deformed Structure in 160Yb.
Creator: Aguilar, Aaron, Riley, Mark A., Safron, Sanford, Capstick, Simon, Rogachev, Grigory, Adams, Todd, Department of Physics, Florida State University
Abstract/Description: The study of nuclear structure at very high angular momentum requires sensitive detector systems in order to detect weak signals. Large gamma-ray arrays were used in this thesis to study the high-spin states in 166;168;170Ta and 160Yb. These arrays were located at facilities such as: Florida State University (FSU), Argonne National Laboratory (ANL), Lawrence Berkeley National Laboratory (LBNL), and Yale University. A study utilizing the Gammasphere spectrometer (the world's most powerful...
Show moreThe study of nuclear structure at very high angular momentum requires sensitive detector systems in order to detect weak signals. Large gamma-ray arrays were used in this thesis to study the high-spin states in 166;168;170Ta and 160Yb. These arrays were located at facilities such as: Florida State University (FSU), Argonne National Laboratory (ANL), Lawrence Berkeley National Laboratory (LBNL), and Yale University. A study utilizing the Gammasphere spectrometer (the world's most powerful array) resulted in a dramatic expansion of over 400 new gamma-ray transitions organized into 29 rotational bands in the level scheme of 170Ta. Alignment behavior, an additivity of Routhians analysis, and B(M1)/B(E2) transition strength ratios are used to support the configuration assignments made for this nucleus. The observation of linking transitions between almost all of the bands allowed the relative excitation energies to be determined for nearly the entire level scheme. All of the above work on 170Ta, resulted in the most comprehensive high-spin level scheme in odd-odd nuclei to date. A significant expansion has also been made to the level scheme of 168Ta using the FSU gamma-ray array. An additivity of alignment analysis, along with a B(M1)/B(E2) analysis made it possible to assign band configurations. Although an experiment studying the high-spin structure of 166Ta using the Yale University spectrometer (YRAST Ball) was performed, detailed analysis resulted in the observation of no new information. A new extremely low intensity band structure has also been observed in 160Yb from another Gammasphere experiment. This structure is interpreted as the first observation of a stable triaxial shape in Yb nuclei.
Show less
Date Issued: 2008
Identifier: FSU_migr_etd-0123
Format: Thesis

Title: Electron Transport in Strongly Correlated Nanostructures.
Creator: Al-Hassanieh, 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 double-level 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 double-level 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 center-of-mass 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 time-dependent density-matrix 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_etd-0149
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 two-particle system interacts, in one dimension, with a target that poses a delta-potential 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 two-particle system interacts, in one dimension, with a target that poses a delta-potential 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 delta-well 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 energy-domain are found to play a dominant and non-perturbative 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 resonance-like 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_etd-0142
Format: Thesis

Title: Coulomb Pseudogaps and Their Role at Metal-Insulator Transitions.
Creator: Mahmoudian, Samiyeh, Dobrosavljević, Vladimir, Dalal, Naresh S., Balicas, Luis, Manousakis, Efstratios, Capstick, Simon, Florida State University, College of Arts and Sciences,...
Show moreMahmoudian, Samiyeh, Dobrosavljević, Vladimir, Dalal, Naresh S., Balicas, Luis, Manousakis, Efstratios, Capstick, Simon, Florida State University, College of Arts and Sciences, Department of Physics
Show less
Abstract/Description: We investigate various fundamental aspects of the metal insulator transition (MIT) by employing several theoretical approaches. Describing the novel features of interacting electronic systems remains one of the principle challenges to theoretical condensed matter physics. Therefore, any effort to provide a deep insight into understanding the nature of MITs opens a new avenue for development of modern technology. First, we present a complete analytical and numerical solution of the Typical...
Show moreWe investigate various fundamental aspects of the metal insulator transition (MIT) by employing several theoretical approaches. Describing the novel features of interacting electronic systems remains one of the principle challenges to theoretical condensed matter physics. Therefore, any effort to provide a deep insight into understanding the nature of MITs opens a new avenue for development of modern technology. First, we present a complete analytical and numerical solution of the Typical Medium Theory (TMT) for the metal-insulator transition. In this theory, we self-consistently calculate the typical amplitude of the electron wave-functions, representing the conceptually simplest order-parameter for the Anderson transition. We classify all possible universality classes for the critical behavior, that can be found within such a mean-field approach. This provides insights into how interaction-induced renormalizations of the disorder potential may produce qualitative modifications of critical behavior. We also formulate a simple description of the leading critical behavior of varies quantities, and then obtain an effective Landau theory for Anderson localization. We also develop an efficient numerical algorithm, "Cluster Typical Medium Theory" (CTMT) to capture both non-local effects and localization in disordered electronic systems. Our formalism utilizes the momentum-resolved typical density of states to characterize the localization transition. We apply this approach to the Anderson model of localization in one and two-dimensions. In one dimension, we find that the critical disorder strength scales inversely with the linear cluster size with a power-law, W[subscript c] ∼ (1/L[subscript c])[superscript 1/v]; whereas in two dimensions, the critical disorder strength decreases logarithmically with the linear cluster size. Our results are in agreement with the one-parameter scaling theory. Furthermore, we show how spatial correlations can also be captured analytically within such a self-consistent theory, by utilizing the standard Landau method of allowing for (slow) spatial fluctuations of the order parameter, and performing an appropriate gradient expansion. Our theoretical results provide insight into recent STM experiments, which were used to visualize the spatially fluctuating electronic wave functions near the metal insulator transition in Ga[subscript 1-x]Mn[subscript x]As.$ We show that, within our theory, all features of the experiment can be accounted for by considering a model of disorder renormalized by long-range Coulomb interactions. This includes the pseudogap formation, the C(R) ∼ 1/R form of the LDOS autocorrelations function, and the ζ ∼ 1/E energy dependence of the correlation length at criticality. In the second part of my Thesis, we show that introducing long-range Coulomb interactions immediately lifts the massive ground state degeneracy induced by geometric frustration for electrons on quarter-filled triangular lattices in the classical limit. Important consequences include the stabilization of a stripe-ordered crystalline (global) ground state, but also the emergence of very many low-lying metastable states with amorphous "stripe-glass" spatial structures. Melting of the stripe order thus leads to a frustrated Coulomb liquid at intermediate temperatures, showing remarkably slow (viscous) dynamics, with very long relaxation times growing in Arrhenius fashion upon cooling, as typical of strong glass formers. On shorter time scales, the system falls out of equilibrium and displays the aging phenomena characteristic of supercooled liquids above the glass transition. Our results show remarkable similarity with the recent observations of charge-glass behavior in ultra-clean triangular organic materials of the θ-(BEDT-TTF)₂ family.
Show less
Date Issued: 2015
Identifier: FSU_2015fall_Mahmoudian_fsu_0071E_12817
Format: Thesis

Title: Non-Abelian 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, two-level 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, two-level 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 so-called 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 non-Abelian anyons, particle-like excitations which satisfy non-Abelian 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 world-lines in 2+1-dimensional 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 non-Abelian 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: Disordered Strongly Correlated Electronic Systems.
Creator: Javan Mard, Hossein, Dobrosavljević, Vladimir, Salters, Vincent J. M., Von Molnar, S. (Stephan), Yang, Kun, Piekarewicz, Jorge, Florida State University, College of Arts and...
Show moreJavan Mard, Hossein, Dobrosavljević, Vladimir, Salters, Vincent J. M., Von Molnar, S. (Stephan), Yang, Kun, Piekarewicz, Jorge, Florida State University, College of Arts and Sciences, Department of Physics
Show less
Abstract/Description: Disorder can have a vast variety of consequences for the physics of phase transitions. Some transitions remain unchanged in the presence of disorder while others are completely destroyed. In this dissertation we study the effects of quenched disorder on electronic systmens at zero temperature. First, we perform variational studies of the interaction-localization problem to describe the interaction-induced renormalizations of the effective (screened) random potential seen by quasiparticles....
Show moreDisorder can have a vast variety of consequences for the physics of phase transitions. Some transitions remain unchanged in the presence of disorder while others are completely destroyed. In this dissertation we study the effects of quenched disorder on electronic systmens at zero temperature. First, we perform variational studies of the interaction-localization problem to describe the interaction-induced renormalizations of the effective (screened) random potential seen by quasiparticles. Here we present results of careful finite-size scaling studies for the conductance of disordered Hubbard chains at half-filling and zero temperature. While our results indicate that quasiparticle wave functions remain exponentially localized even in the presence of moderate to strong repulsive interactions, we show that interactions produce a strong decrease of the characteristic conductance scale g* signaling the crossover to strong localization. This effect, which cannot be captured by a simple renormalization of the disorder strength, instead reflects a peculiar non-Gaussian form of the spatial correlations of the screened disordered potential, a hitherto neglected mechanism to dramatically reduce the impact of Anderson localization (interference) effects. Second, we formulate a strong-disorder renormalization-group (SDRG) approach to study the beta function of the tight-binding model in one dimension with both diagonal and off-diagonal disorder for states at the band center. We show that the SDRG method, when used to compute transport properties, yields exact results since it is identical to the transfer matrix method. The beta function is shown to be universal when only off-diagonal disorder is present even though single-parameter scaling is known to be violated. A different single-parameter scaling theory is formulated for this particular (particle-hole symmetric) case. Upon breaking particle-hole symmetry (by adding diagonal disorder), the beta function is shown to crossover from the universal behavior of the particle-hole symmetric case to the conventional nonuniversal one in agreement with the two-parameter scaling theory. We finally draw an analogy with the random transverse-field Ising chain in the paramagnetic phase. The particle-hole symmetric case corresponds to the critical point of the quantum Ising model, while the generic case corresponds to the Griffiths paramagnetic phase. Finally, we implement an efficient strong-disorder renormalization-group (SDRG) procedure to study disordered tight-binding models in any dimension and on the Erdos- Renyi random graphs, which represent an appropriate infinite dimensional limit. Our SDRG algorithm is based on a judicious elimination of most (irrelevant) new bonds generated under RG. It yields excellent agreement with exact numerical results for universal properties at the critical point without significant increase of computer time, and confirm that, for Anderson localization, the upper critical dimension duc = infinite. We find excellent convergence of the relevant 1/d expansion down to d = 2, in contrast to the conventional 2 + ε expansion, which has little to say about what happens in any d [greater than] 3. We show that the mysterious mirror symmetry of the conductance scaling function is a genuine strong-coupling effect, as speculated in early work. This opens an efficient avenue to explore the critical properties of Anderson transition in the strong-coupling limit in high dimensions.
Show less
Date Issued: 2015
Identifier: FSU_2015fall_JavanMard_fsu_0071E_12907
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: FeSi1-xGex, Ce1-xLaxCoIn5, and Yb1-xYxInCu4. For FeSi1-xGex, we constructed the phase diagram through the analysis of magnetic, thermal and transport measurements on single crystals. The phase diagram shows a first-order 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: FeSi1-xGex, Ce1-xLaxCoIn5, and Yb1-xYxInCu4. For FeSi1-xGex, we constructed the phase diagram through the analysis of magnetic, thermal and transport measurements on single crystals. The phase diagram shows a first-order 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 Ce1-xLaxCoIn5, 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 Ce1-xLaxCoIn5, 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 Ce1-xLaxCoIn5 alloys has a peak around 70K, suggesting the same crystalline field splittings occurs the alloy series Ce1-xLaxCoIn5. 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 non-Fermi liquid behavior for Ce rich region. For Yb1-xYxInCu4, 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 magneto-resistance 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_etd-0646
Format: Thesis

Title: Dynamics of Biomolecules, Ligand Binding & Biological Functions.
Creator: Yi, Myunggi, Zhou, Huan-xiang, Logan, Timothy M., Berg, Bernd A., Xiong, Peng, Nymeyer, Hugh, Department of Physics, Florida State University
Abstract/Description: Proteins are flexible and dynamic. One static structure alone does not often completely explain biological functions of the protein, and some proteins do not even have high resolution structures. In order to provide better understanding to the biological functions of nicotinic acetylcholine receptor, Diphtheria toxin repressor and M2 proton channel, the dynamics of these proteins are investigated using molecular modeling and molecular dynamics (MD) simulations. With absence of high resolution...
Show moreProteins are flexible and dynamic. One static structure alone does not often completely explain biological functions of the protein, and some proteins do not even have high resolution structures. In order to provide better understanding to the biological functions of nicotinic acetylcholine receptor, Diphtheria toxin repressor and M2 proton channel, the dynamics of these proteins are investigated using molecular modeling and molecular dynamics (MD) simulations. With absence of high resolution structure of alpha 7 receptor, the homology models of apo and cobra toxin bound forms have been built. From the MD simulations of these model structures, we observed one subunit of apo simulation moved away from other four subunits. With local movement of flexible loop regions, the whole subunit tilted clockwise. These conformational changes occurred spontaneously, and were strongly correlated with the conformational change when the channel is activated by agonists. Unlike other computational studies, we directly compared our model of open conformation with the experimental data. However, the subunits of toxin bound form were stable, and conformational change is restricted by the bound cobra toxin. These results provide activation and inhibition mechanisms of alpha 7 receptors and a possible explanation for intermediate conductance of the channel. Intramolecular complex of SH3-like domain with a proline-rich (Pr) peptide segment in Diphtheria toxin repressor (DtxR) is stabilized in inactive state. Upon activation of DtxR by transition metal binding, this intramolecular complex should be dissociated. The dynamics of this intramolecular complex is investigated using MD simulations and NMR spectroscopy. We observed spontaneous opening and closing motions of the Pr segment binding pockets in both Pr-SH3 and SH3 simulations. The MD simulation results and NMR relaxation data suggest that the Pr segment exhibits a binding ¡ê unbinding equilibrium. Despite a wealth of experimental validation of Gouy-Chapman (GC) theory to charged lipid membranes, a test of GC theory by MD simulations has been elusive. Here we demonstrate that the ion distributions at different salt concentrations in anionic lipid bilayer systems agree well with GC predictions using MD simulations. Na+ ions are adsorbed to the bilayer through favorable interactions with carbonyls and hydroxyls, reducing the surface charge density by 72.5%. The interactions of amantadine, an antiinfluenza A drug, with DMPC bilayers are investigated by an MD simulation and by solid-state NMR. The MD simulation results and NMR data demonstrate that amantadine is located within the interfacial region with upward orientation and interacts with the lipid headgroup and glycerol backbone, while the adamantane group of amantadine interacts with the glycerol backbone and much of fatty acyl chain, as it wraps underneath of the drug. The lipid headgroup orientation is influenced by the drug as well. The recent prevalence of amantadine-resistant mutants makes a development of new drug urgent. The mechanism of inhibition of M2 proton channel in influenza virus A by amantadine is investigated. In the absence of high resolution structure, we model the apo and drug bound forms based on NMR structures. MD simulations demonstrate that channel pore is blocked by a primary gate formed by Trp41 helped by His37 and a secondary gate formed by Val27. The blockage by the secondary gate is extended by the drug bound just below the gate, resulting in a broken water wire throughout the simulation, suggesting a novel role of Val27 in the inhibition by amantadine. Recent X-ray structure validates the simulation results.
Show less
Date Issued: 2008
Identifier: FSU_migr_etd-0661
Format: Thesis

Title: J/Psi -> E+E- Measurements in Cu + Cu Collisions at 200 Gev.
Creator: Das, Kushal, Crede, Volker, Safron, Sanford, Frawley, Anthony D., Capstick, Simon, Baer, Howie, Department of Physics, Florida State University
Abstract/Description: High-energy heavy-ion collisions are a powerful tool in the laboratory to investigate the phase transition from ordinary nuclear matter to a deconfined state of quarks and gluons, called the Quark-Gluon Plasma (QGP), which is predicted to be formed above a temperature of order Tc ~ 170 MeV in lattice Quantum Chromodynamics (QCD). Suppression of J/Ï production has long been considered to be one of the most promising signatures for the deconfinement of matter. J/Ï production has been measured...
Show moreHigh-energy heavy-ion collisions are a powerful tool in the laboratory to investigate the phase transition from ordinary nuclear matter to a deconfined state of quarks and gluons, called the Quark-Gluon Plasma (QGP), which is predicted to be formed above a temperature of order Tc ~ 170 MeV in lattice Quantum Chromodynamics (QCD). Suppression of J/Ï production has long been considered to be one of the most promising signatures for the deconfinement of matter. J/Ï production has been measured by the PHENIX experiment, one of the two major experiments at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory (BNL) in p + p, d + Au, Au + Au and Cu + Cu collisions at the center of mass energy per nucleon (âsNN) of 200 GeV. The analysis of the Cu + Cu data is the focus of this dissertation. Yields of J/Psi production in Cu + Cu collisions at âsNN = 200 GeV have been measured by the PHENIX experiment over the rapidity range |y|
Show less
Date Issued: 2008
Identifier: FSU_migr_etd-0835
Format: Thesis

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

Title: Study of Shashlik Detector Performance Under High Particle Pileup.
Creator: Jones, Spencer, Department of Physics
Date Issued: 2013
Identifier: FSU_migr_undergradresearch-0029
Format: Citation

Title: Adaptation of Ultra-Precise Atomic Mass Measurement Techniques to Microwave Spectroscopy on a Single Molecular Ion by Detecting Polarizability Shifts in a Penning Trap.
Creator: Zarrella, Andrew, Physics
Abstract/Description: Using the FSU Ion Penning trap it is possible to measure the ratio of the cyclotron frequencies of two molecular ions to a precision of 0.1 ppb. These cyclotron frequencies can be shifted due to large electric polarizabilities in some molecular ions. Because the polarizability of the molecular ion is dependent on the quantized rotational levels of the molecule, is possible to use the cyclotron frequency shifts detected in our lab to detect transitions between rotational levels. This allows us...
Show moreUsing the FSU Ion Penning trap it is possible to measure the ratio of the cyclotron frequencies of two molecular ions to a precision of 0.1 ppb. These cyclotron frequencies can be shifted due to large electric polarizabilities in some molecular ions. Because the polarizability of the molecular ion is dependent on the quantized rotational levels of the molecule, is possible to use the cyclotron frequency shifts detected in our lab to detect transitions between rotational levels. This allows us to do microwave spectroscopy on single molecular ions. The main goal of this project will be to implement this new method of microwave spectroscopy, by measuring the lambda-type doubling splitting of the diatomic molecular ion, NH+, in its vibrational and rotational ground state.
Show less
Date Issued: 2011
Identifier: FSU_migr_uhm-0043
Format: Thesis

Title: Validating Monte-Carlo Distributions in the Search for the Higgs Boson.
Creator: Ackert, Andrew, Physics
Abstract/Description: The goal of this research was to develop a method of validating multi-parameter Monte- Carlo (MC) simulations. These simulations mimic the proton-proton collisions at the Large Hadron Collider (LHC) that are being used to search for the Higgs boson. The basic idea is to construct partitions, count the number of data points that lie within each partition, and apply the partition and counting procedures to both collision data from the LHC and data created via Monte-Carlo simulations. In...
Show moreThe goal of this research was to develop a method of validating multi-parameter Monte- Carlo (MC) simulations. These simulations mimic the proton-proton collisions at the Large Hadron Collider (LHC) that are being used to search for the Higgs boson. The basic idea is to construct partitions, count the number of data points that lie within each partition, and apply the partition and counting procedures to both collision data from the LHC and data created via Monte-Carlo simulations. In principle, the method developed can be used with any measure of dissimilarity between distributions with any number of parameters. In this study, we used Fisher's test (F-test) applied to 2 parameters of the data (btag and di-muon mass). Through the F-test it was concluded that, at least in these 2 parameters, the LHC data and the MC data were in agreement.
Show less
Date Issued: 2012
Identifier: FSU_migr_uhm-0104
Format: Thesis

Title: Synthesis and Characterization of SN Doped CEIN3.
Creator: Collar, Kristen, Physics
Abstract/Description: CeIn3 is a cubic antiferromagnetic heavy fermion metal that orders with a Néel temperature of 10.1K at zero magnetic field. It requires fields up to 64T in order to see the Néel transition and the modified Lifshitz transition[1,2]; however, low dopings of tin have been shown to greatly reduce the Néel transition to occur at lower magnetic fields[3]. CeIn3-xSnx (x=0.25, 0.50, 0.75) were grown using a flux growth technique to investigate the magnetic transitions in lower fields. Crystal...
Show moreCeIn3 is a cubic antiferromagnetic heavy fermion metal that orders with a Néel temperature of 10.1K at zero magnetic field. It requires fields up to 64T in order to see the Néel transition and the modified Lifshitz transition[1,2]; however, low dopings of tin have been shown to greatly reduce the Néel transition to occur at lower magnetic fields[3]. CeIn3-xSnx (x=0.25, 0.50, 0.75) were grown using a flux growth technique to investigate the magnetic transitions in lower fields. Crystal analysis was conducted using SEM/EDS, which estimated the atomic percentages of the elements in the compound to quantify the amount of tin that was incorporated into each crystal. The crystals were characterized using torque magnetometry in the Physical Property Measurement System (PPMS) in order to observe de Haas-van Alphen (dHvA) quantum oscillations. The dHvA oscillations observed in the CeIn3 yielded frequencies which correspond to the Landau levels being excited past the Fermi energy. The frequencies were found using a fast fourier transform. They were confirmed to be the same frequencies seen in published data [4], which verifies that this method of flux growth has the potential to grow clean single crystals. No oscillations were observed in the tin doped samples. It was concluded that the sample doping levels were too high and acted as a contaminant, preventing the dHvA oscillations from being observed. The search for an optimum doping continues with lower doping concentrations being grown.
Show less
Date Issued: 2011
Identifier: FSU_migr_uhm-0007
Format: Thesis

Title: Structure of the atomic nucleus around 16 O.
Creator: Crisp, Amy
Date Issued: 2007
Identifier: 160848, FSDT160848, fsu:19104
Format: Document (PDF)

Title: The study of inclinometers in a magnetic field for use at CERN.
Creator: Pouliot, Stacy L.
Date Issued: 2004-01-01
Identifier: 160359, FSDT160359, fsu:18874
Format: Document (PDF)

Title: An Exploration into the Photoproduction of Proton-Antiproton Pairs.
Creator: Morales, Peter, Physics
Abstract/Description: The research focus of this report is an analysis on the reaction γp→ppp̄, for photon energy in the range 4.8 to 5.5 GeV. The purpose of this study is to gain a greater understanding of the processes behind the photoproduction of proton-antiproton pairs. Research was performed on data collected from the g12 experiment conducted at Jefferson National Laboratory Accelerator Facility. Data from the experiment was mined and formatted for analysis in the ROOT framework. Cuts were made to the data...
Show moreThe research focus of this report is an analysis on the reaction γp→ppp̄, for photon energy in the range 4.8 to 5.5 GeV. The purpose of this study is to gain a greater understanding of the processes behind the photoproduction of proton-antiproton pairs. Research was performed on data collected from the g12 experiment conducted at Jefferson National Laboratory Accelerator Facility. Data from the experiment was mined and formatted for analysis in the ROOT framework. Cuts were made to the data to ensure events had protons with well-defined momenta and minimal background. A total of 20,927 events were observed. Invariant mass plots were generated from the selected data for each proton and antiproton in order to search for intermediate resonances that might decay to a proton-antiproton pair. There were no significant signs of narrow resonances found in the final data. However, the possibility for broader resonances is not completely left out.
Show less
Date Issued: 2012
Identifier: FSU_migr_uhm-0073
Format: Thesis

Title: Lagrange Meshes in Hardronic Physics.
Creator: Bryant, Brandon, Physics
Abstract/Description: In hadronic physics, the potentials of hadrons are not known and, therefore, their wave functions are not known either. The wave functions can be used to calculate energy spectra and other properties of hadrons, like decay rates. Some hadronic physicists resort to approximation methods to describe the wave functions. In this project, we express wave functions as expansions of basis functions that contain orthogonal polynomials and then employ them in a variational method. We apply this...
Show moreIn hadronic physics, the potentials of hadrons are not known and, therefore, their wave functions are not known either. The wave functions can be used to calculate energy spectra and other properties of hadrons, like decay rates. Some hadronic physicists resort to approximation methods to describe the wave functions. In this project, we express wave functions as expansions of basis functions that contain orthogonal polynomials and then employ them in a variational method. We apply this technique to 2 different systems with known wave functions for 2 different bases. We find that with an appropriately chosen basis of sufficient size this technique produces accurate wave functions and energy spectra. Choosing a sufficiently large basis becomes problematic in practice because of the computational time required to perform eigenvalue calculations. It is desirable then to employ an efficient means of computation. We address this issue by use of the Lagrange mesh method. This method is an approximate variational calculation that gives a potential matrix which is diagonal and a kinetic matrix that must only be calculated once for a given basis. Furthermore, each nonzero element in the potential matrix requires evaluation at only 1 mesh point and each element in the kinetic matrix requires evaluation at only 1 or 2 mesh points. We apply the Lagrange mesh method to a problem with an exact, known solution and then to a hadronic problem. We find that this method is easily implemented and gives accurate results.
Show less
Date Issued: 2011
Identifier: FSU_migr_uhm-0006
Format: Thesis

Title: Investigation of the structure of the neutron rich nucleus 25NE.
Creator: Padgett, Stephen
Date Issued: 2006-05-23
Identifier: 160337, FSDT160337, fsu:18863
Format: Document (PDF)

Title: Monte Carlo Simulations for Future Geoneutrino Detectors.
Creator: Askins, Morgan, Physics
Abstract/Description: The main contribution of heat in the earth's mantle is thought to be the radioactive decays of 238U, 232Th, and 40K decay series. A precise measurement of the levels of 238U and 232Th can be determined by measuring the flux of ve (geoneutrinos) emitted from their decay chains. Although detectors such as kamLAND and Borexino have detected few geoneutrinos, a new cost effective geoneutrino detector is proposed which takes advantage of the total internal re ection within a long rectangular prism...
Show moreThe main contribution of heat in the earth's mantle is thought to be the radioactive decays of 238U, 232Th, and 40K decay series. A precise measurement of the levels of 238U and 232Th can be determined by measuring the flux of ve (geoneutrinos) emitted from their decay chains. Although detectors such as kamLAND and Borexino have detected few geoneutrinos, a new cost effective geoneutrino detector is proposed which takes advantage of the total internal re ection within a long rectangular prism acrylic container of liquid scintillator having a single photomultiplier tube (PMT) on each end. An array of these containers would allow for a large scintillator volume relative to the number of PMTs, but a design with such a large ratio of arcylic to scintillator may suffer from a larger background from naturally occurring 238U and 232Th within the acrylic. The event signatures of these decays were compared to those from neutrino interactions using RAT, a Monte Carlo simulation software based upon GEANT4. Implimentation of detector design allowed for cuts in background decays from the detector to be made such that 93% of the background 238U and 86% of the background 232Th decay series are removed. The overall loss of neutrino events from these cuts is about 36%.
Show less
Date Issued: 2011
Identifier: FSU_migr_uhm-0003
Format: Thesis

Title: Precision atomic mass measurements using single ions in a Penning trap.
Creator: Wingfield, Elizabeth
Date Issued: 2007-07-13
Identifier: 160904, FSDT160904, fsu:19132
Format: Document (PDF)

Title: The nuclear structure of 21F from the 10Be(14C,t)21F reaction and shell model validity for neutron-rich nuclei.
Creator: Perry,Michelle
Date Issued: 2007-07-13
Identifier: 160768, FSDT160768, fsu:19066
Format: Document (PDF)

Title: Digitally Controlled Four Harmonic Buncher for FSU LINAC.
Creator: Moerland, Daniel, Physics
Abstract/Description: Florida State University's John D. Fox Superconducting Accelerator Laboratory is operating a Tandem-LINAC system for heavy ion beams at energies of 5-10 MeV/u. Recently, the accelerator has been used as the driver for the radioactive beam facility RESOLUT, which poses new demands on its high-intensity performance and time-resolution. These demands motivated us to optimize the RF bunching system and to switch the bunch frequency from 48.5 to 12.125MHz. We installed a four-harmonic resonant...
Show moreFlorida State University's John D. Fox Superconducting Accelerator Laboratory is operating a Tandem-LINAC system for heavy ion beams at energies of 5-10 MeV/u. Recently, the accelerator has been used as the driver for the radioactive beam facility RESOLUT, which poses new demands on its high-intensity performance and time-resolution. These demands motivated us to optimize the RF bunching system and to switch the bunch frequency from 48.5 to 12.125MHz. We installed a four-harmonic resonant transformer to create 3-4 kV potential oscillations across a pair of wire-mesh grids. This setup is modulating the energy of the beam injected into the tandem accelerator, with the aim to create short bunches of beam particles. A sawtooth-like wave-form is created using the Fourier series method, by combining the basis sinusoidal wave of 12.125MHz and its 3 higher order harmonics, in a manner similar to the systems used at ATLAS [1] and other RF-accelerators. A new aspect of our setup is the use of a digital 1GHz function generator, which allows us to optimize and stabilize the synthesized waveform. The control system was realized using Labview [2] and integrated into the recently updated controls of the accelerator. We characterize the bunching quality achieved and discuss the optimization of the bunching wave-form. The bunching system has been successfully used in a number of LINAC-experiments performed during 2011 and 2012.
Show less
Date Issued: 2012
Identifier: FSU_migr_uhm-0106
Format: Thesis

Title: Lagrange Meshes in Nuclear Physics.
Creator: Hynds, Taylor, Department of Physics
Abstract/Description: We examine different methods of solving the Schroedinger equation for two and three-body systems. We begin by constructing variational wave functions as expansions in a basis of orthogonal polynomials. This method has been found to give accurate results, given a sufficiently large basis. However, computationally this can become very cumbersome. We therefore employ the Lagrange-mesh method, which leads to a simple calculation of both potential and kinetic matrix elements that is both...
Show moreWe examine different methods of solving the Schroedinger equation for two and three-body systems. We begin by constructing variational wave functions as expansions in a basis of orthogonal polynomials. This method has been found to give accurate results, given a sufficiently large basis. However, computationally this can become very cumbersome. We therefore employ the Lagrange-mesh method, which leads to a simple calculation of both potential and kinetic matrix elements that is both computationally efficient and results in little to no loss in accuracy. This method has been applied to several problems with well known analytical solutions, and has given excellent results. We demonstrate the efficacy of this method in analyzing nuclear systems.
Show less
Date Issued: 2013
Identifier: FSU_migr_uhm-0177
Format: Thesis

Title: Finite Lattice Size Corrections The Energy-Momentum Dispersion.
Creator: McDargh, Zachary, Physics
Abstract/Description: Lattice Gauge Theory (LGT) describes gauge and matter fields on a discrete Euclidian space-time lattice. Due to the finite spacing between the lattice points, there is a built-in ultra-violet energy cutoff. Additionally, there is an infrared energy cutoff in computer simulations due to the finite size of the lattice. With these approximations, the energy-momentum dispersion becomes modified. In this thesis, we study the recovery of the continuous energy-momentum dispersion. We perform fits of...
Show moreLattice Gauge Theory (LGT) describes gauge and matter fields on a discrete Euclidian space-time lattice. Due to the finite spacing between the lattice points, there is a built-in ultra-violet energy cutoff. Additionally, there is an infrared energy cutoff in computer simulations due to the finite size of the lattice. With these approximations, the energy-momentum dispersion becomes modified. In this thesis, we study the recovery of the continuous energy-momentum dispersion. We perform fits of the correlation function fromMarkov ChainMonte Carlo (MCMC) simulations for various lattice sizes and spacings for a free-scalar field and for an Abelian U(1) gauge field. For the scalar field, we also vary the mass of the particles; for U(1) LGT, we vary the coupling constant β. These fits return the energy of a particle at definite momentum, from which the mass can be recovered using the energy-momentum dispersion. It is found that the finite-size effect in MCMC calculations decreases as exp(−N), where N is the space dimension of the lattice. Furthermore, the effect is more significant for larger masses (scalar field) and coupling constant values near the phase transition βc = 1.01 (U(1) LGT).
Show less
Date Issued: 2012
Identifier: FSU_migr_uhm-0047
Format: Thesis

Title: Exploratory Studies of the Photoproduced π°η Channel and Determination of Preliminary Cross Sections.
Creator: Woodard, Anna
Abstract/Description: The Crystal Barrel detector is an ideal instrument to study multi-photon final states due to its large solid angle coverage and excellent photon detection efficiency. In this study, preliminary differential cross sections of the reaction γp → Δη→ pπ°η were extracted from data taken while the Crystal Barrel was configured with the TAPS calorimeter positioned in the forward direction. Approximately 186,000 pπ°η events were identified. Trigger efficiencies and energy thresholds in the TAPS...
Show moreThe Crystal Barrel detector is an ideal instrument to study multi-photon final states due to its large solid angle coverage and excellent photon detection efficiency. In this study, preliminary differential cross sections of the reaction γp → Δη→ pπ°η were extracted from data taken while the Crystal Barrel was configured with the TAPS calorimeter positioned in the forward direction. Approximately 186,000 pπ°η events were identified. Trigger efficiencies and energy thresholds in the TAPS calorimeter were studied. Events were reconstructed using a missing proton kinematic fit and the pπ°η final state was selected via a series of confidence level cuts. pπ°η events were classified according to incoming photon energy Eγ and scattering angle θηcm of the η meson in the center-of-mass system. Invariant mass spectra for the p_0 combinations (Eγ, cos θηcm) were plotted. Existing Monte Carlo (MC) software was used to simulate the experimental set-up and generate the expected mass spectra, corrected for phasespace and relativistic effects, for major contributing channels. A root C interpreter script was written to determine the Δ reaction yields as a function of the incoming photon energy and scattering angle. This was accomplished by using the roofit modeling toolkit to generate probability density functions (PDFs) from the MC. The pπ° spectra were then fitted with a sum of MC PDFs for the two largest isobar contributions, Δ+(1232)π and N(1535)S11η. The pπ° spectra indicate dominant Δ production in the threshold region. At higher energies the S11 contribution increases; the development of a second peak besides the Δ becomes visible around 1550 MeV. Above 1800 MeV, S11 production is comparable in intensity to the Δ. An unambiguous angular dependence for the S11 is observed over the full Eγ range as production drops off rapidly at forward angles. The fit procedure is more accurate at higher energies, where Δ and S11 production are well separated, and two clear peaks exist. It is likely that at lower energies the background under the Δ peak was underestimated. Preliminary differential cross sections for γp → Δη → pπ°η were calculated from the Δ yields and are presented here along with an interpretation of major features. First results forthe total γp → pπ°η and γp → pπ°π° cross sections are included. Agreement with previous studies is fair. Possible explanations for discrepancies are discussed.
Show less
Date Issued: 2008
Identifier: FSU_migr_uhm-0045
Format: Thesis

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

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

Theses and Dissertations (1151)	+ -
Digitized Theses and Dissertations (841)	+ -
Paul A.M. Dirac Collection (159)	+ -
FSU Photograph Collection (82)	+ -
Undergraduate Honors Theses (52)	+ -

Jewell Genevieve Cooper Scrapbook, ca. 1924-1930 (24)	+ -
Historical Undergraduate Honors Theses (7)	+ -
Publications (5)	+ -
Department of Biomedical Sciences (2)	+ -
Department of Chemistry and Biochemistry (2)	+ -
Department of Family Medicine and Rural Health (2)	+ -
Department of Nutrition, Food and Exercise Sciences (2)	+ -
Carolyne Doyle Richardson Scrapbook, ca. 1926 (2)	+ -
Showcase of Undergraduate Research Excellence (2)	+ -
Department of Behavioral Sciences and Social Medicine (1)	+ -
Department of Biological Science (1)	+ -
Department of Educational Psychology and Learning Systems (1)	+ -
Department of Mathematics (1)	+ -
Department of Physics (1)	+ -
L. Janet Wells Scrapbook Collection, 1938-1942 (1)	+ -
Doak S. Campbell Collection (1)	+ -
Department of Physics (1)	+ -
Institute of Sports Sciences & Medicine (1)	+ -
Program in Neuroscience (1)	+ -

Physics (440)	+ -
Education, Physical (227)	+ -
Physics, Nuclear (162)	+ -
Mathematics (104)	+ -
Chemistry, Physical (103)	+ -

Physics, Atmospheric Science (103)	+ -
Science (83)	+ -
Florida State College for Women (70)	+ -
Physical Oceanography (69)	+ -
Physical Education Department (59)	+ -
Physics, Condensed Matter (59)	+ -
Writing (53)	+ -
Physics, Elementary Particles and High Energy (47)	+ -
Correspondence (45)	+ -
Physicists (44)	+ -
Florida State University (42)	+ -
Chemistry, Physical and theoretical (35)	+ -
Nuclear physics (32)	+ -
Autrey, Elizabeth (29)	+ -
Physics, Department of (29)	+ -
Geometry (28)	+ -
Physics, Molecular (27)	+ -
Autrey, Katharine (26)	+ -
Cooper, Jewell Genevieve (24)	+ -
Cooper, Judy Genevieve (24)	+ -
Physics, General (22)	+ -
Tumbling Class (22)	+ -
Condensed matter (20)	+ -
Physics, Fluid and Plasma (16)	+ -
Biophysics (15)	+ -

Schwartz, Guenter (5)	+ -
Florida State University (2)	+ -
Schwarz, Guenter (2)	+ -
Deslattes, Richard D. (1)	+ -
Dirac, P. A. M. (Paul Adrien Maurice) (1)	+ -

Search In

Pages

Pages

Sort Results By:

Narrow results by:

Collection

Topical Subject

Name as Subject

Geographic Subject

Temporal Subject

Genre Subject

Genre

Type of Resource

Language

Creator

Format

Found In

Location

Owner

1920-1930 (36)	+ -
1930-1940 (26)	+ -
1940-1950 (2)	+ -

text (1377)	+ -
still image (112)	+ -

English (679)	+ -
French (4)	+ -
German (4)	+ -
fra (1)	+ -