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Full-Text Articles in Physical Sciences and Mathematics

Computational Simulations Of Temperature-Dependent Dynamics In Type Ii Superconductors Using A Material Specific Formulation Of Ginzburg Landau Theory, Aiden Harbick May 2020

Computational Simulations Of Temperature-Dependent Dynamics In Type Ii Superconductors Using A Material Specific Formulation Of Ginzburg Landau Theory, Aiden Harbick

Undergraduate Honors Theses

Superconducting Radio Frequency (SRF) cavities play a fundamental role in particle accelerators. Efficient operation depends on expelling magnetic flux from the cavity, and any residual flux that remains trapped after cooling below the critical temperature can have a significant impact on performance. Experimental evidence suggests that material defects as well as cooling protocols can have a strong impact on subsequent performance. To better understand these phenomena, we use time-dependent Ginzburg-Landau theory implemented as finite-element simulations. We adapt the theory to allow spatial variation of material-specific parameters along with realistic temperature dependencies. We report on numerical experiments for different configurations of ...


Chiral Transport In Anisotropic Materials, Jacopo Gliozzi May 2019

Chiral Transport In Anisotropic Materials, Jacopo Gliozzi

Undergraduate Honors Theses

Chiral materials are a class of systems in which the momentum of quasiparticles is coupled to a pseudospin degree of freedom, thus affecting their transport properties. In particular, such materials can exhibit Klein tunneling, in which chiral particles tunnel through a potential barrier with probability one due to a suppression of backscattering. In chiral materials with an anisotropic band structure, this tunneling depends nontrivially on the interplay between chirality and the direction of dispersion.

We discuss the consequences of transport in a minimal chiral anisotropic model, highlighting the role of the pseudospin in scattering through a Klein barrier. We implement ...


Strong Electron-Boson Coupling In The Iron-Based Superconductor Bafe1.9pt0.1as2 Revealed By Infrared Spectroscopy, Mumtaz M. Qazilbash Dec 2018

Strong Electron-Boson Coupling In The Iron-Based Superconductor Bafe1.9pt0.1as2 Revealed By Infrared Spectroscopy, Mumtaz M. Qazilbash

Arts & Sciences Articles

No abstract provided.


Exotic Phases In Attractive Fermions: Charge Order, Pairing, And Topological Signatures, Peter Rosenberg Jul 2018

Exotic Phases In Attractive Fermions: Charge Order, Pairing, And Topological Signatures, Peter Rosenberg

Dissertations, Theses, and Masters Projects

Strongly interacting many-body systems remain a central challenge of modern physics. Recent developments in the field of ultra-cold atomic physics have opened a new window onto this enduring problem. Experimental progress has revolutionized the approach to studying many-body systems and the exotic behaviors that emerge in these systems. It is now possible to engineer and directly measure a variety of models that can capture the essential features of real materials without the added complexity of disorder, impurities, or complicated or irregular geometries. The parameters of these models can be freely tuned with tremendous precision. These experimental realizations are an ideal ...


Enhancing The Capabilities Of Infrared Microscopy Apparatus, Ryan Wilmington May 2018

Enhancing The Capabilities Of Infrared Microscopy Apparatus, Ryan Wilmington

Undergraduate Honors Theses

My honors research consists of the design and optimization of a microscopy apparatus as an accessory to an existing macroscopic spectroscopy setup. Using this apparatus, spot sizes below 30 microns can be obtained with high enough intensity to measure infrared-active phonon features. In addition the main optical apparatus, I have developed electronic connections to interface to a mid-infrared detector, a purge gas housing to eliminate contamination from atmospheric vibrational resonances, and a sample stage with sub-micron precision translation to properly operate the apparatus in purge.


Highly Repeatable Nanoscale Phase Coexistence In Vanadium Dioxide Films, Mumtaz M. Qazilbash Feb 2018

Highly Repeatable Nanoscale Phase Coexistence In Vanadium Dioxide Films, Mumtaz M. Qazilbash

Arts & Sciences Articles

No abstract provided.


Superconducting Thin Films For The Enhancement Of Superconducting Radio Frequency Accelerator Cavities, Matthew Burton Nov 2017

Superconducting Thin Films For The Enhancement Of Superconducting Radio Frequency Accelerator Cavities, Matthew Burton

Dissertations, Theses, and Masters Projects

Bulk niobium (Nb) superconducting radio frequency (SRF) cavities are currently the preferred method for acceleration of charged particles at accelerating facilities around the world. However, bulk Nb cavities have poor thermal conductance, impose material and design restrictions on other components of a particle accelerator, have low reproducibility and are approaching the fundamental material-dependent accelerating field limit of approximately 50MV/m. Since the SRF phenomena occurs at surfaces within a shallow depth of ~1 µm, a proposed solution to this problem has been to utilize thin film technology to deposit superconducting thin films on the interior of cavities to engineer the ...


Infrared Spectroscopy And Nano-Imaging Of La0.67sr0.33mno3 Films, Peng Xu May 2017

Infrared Spectroscopy And Nano-Imaging Of La0.67sr0.33mno3 Films, Peng Xu

Dissertations, Theses, and Masters Projects

Charge transport properties of manganites can be significantly modified by temperature, chemical doping, strain, and interfacial boundaries. In this dissertation, we report studies on broadband far-field infrared spectroscopy and near-field infrared imaging of single crystalline thin films of Sr doped manganite LaMnO3 at 0.33 doping level. at this Sr-doping level, the manganite films undergo a phase transition between a ferromagnetic metallic phase at low temperatures to a paramagnetic, insulating phase at higher temperatures. The films were grown on different substrates with different thicknesses by pulsed laser deposition method. The temperature dependent far-field infrared data on 85 nm thick La0 ...


Persistent Population Biases In Branching Random Walk Algorithms, David J. Geroski May 2015

Persistent Population Biases In Branching Random Walk Algorithms, David J. Geroski

Undergraduate Honors Theses

We explore the existence of a residual population bias in Diffusion Monte Carlo algorithms. We develop a model problem, which mimics the single-particle, one dimensional simple harmonic oscillator of unitary ground state energy, to study these biases. We then apply an importance sampling algorithms with a population of a single random walker to calculate the ground state energy and wavefunction of our modeled system in cases of both perfect and imperfect importance sampling. In the former case, we perfectly calculate both the ground state energy and corresponding wavefunction of our system, thus validating our calculations and assumed answer. In the ...


Growth And Characterization Of Gold Nanostructures Produced From Diatomaceous Algae, David A. Specht May 2015

Growth And Characterization Of Gold Nanostructures Produced From Diatomaceous Algae, David A. Specht

Undergraduate Honors Theses

Silica nanostructures (frustules) grown by the algae Thalassiosira eccentrica can be used to template the production of regular arrays of supported gold nanodots, with sizes ranging from 30 to 50 nm. This growth is of particular interest because it represents a novel and efficient way to produce and distribute nanoparticles, particularly for applications in catalysis, and may demonstrate a value for a byproduct ash produced when diatomaceous algae is used to produce biofuel. Growth has been characterized by both SEM and AFM imagery. This growth of regular nanoparticles has also been demonstrated with carbon evaporation, and may be a means ...


Ultracold Rubidium And Potassium System For Atom Chip-Based Microwave And Rf Potentials, Austin R. Ziltz Jan 2015

Ultracold Rubidium And Potassium System For Atom Chip-Based Microwave And Rf Potentials, Austin R. Ziltz

Dissertations, Theses, and Masters Projects

In this dissertation we study the development of microwave and RF near-field potentials for use with atom chip trapped atomic gases. These potentials are inherently spin-dependent, able to target individual spin states simultaneously. In contrast with traditional atom chip potentials, these RF traps can be operated at arbitrary bias magnetic field strengths and thus be combined with magnetic Feshbach resonances. Furthermore, these potentials can strongly suppress the potential roughness that plagues traditional atom chip potentials. We present a dual chamber atom chip apparatus for generating ultracold 87Rb and 39K atomic gases. The apparatus produces quasi-pure Bose-Einstein condensates of 104 87Rb ...


Electronic Properties Of Chiral Two-Dimensional Materials, Christopher Lawrence Charles Triola Jan 2015

Electronic Properties Of Chiral Two-Dimensional Materials, Christopher Lawrence Charles Triola

Dissertations, Theses, and Masters Projects

In this dissertation we study the electronic properties of certain two-dimensional chiral electron systems. We study the static and dynamic screening of gapped bilayer graphene and find important qualitative differences between the dielectric screening function obtained using a simplified 2-band model and that obtained using a more sophisticated 4-band model. We also formulate a continuum model to study the low-energy electronic properties of heterostructures formed by graphene on a strong three-dimensional topological insulator (TI) both for the case of commensurate and incommensurate stacking. We find that the proximity of the TI induces a strong enhancement of the spin-orbit coupling in ...


Spectroscopic Ellipsometry And Cryogenic Capability, Arlough Hollingshad May 2014

Spectroscopic Ellipsometry And Cryogenic Capability, Arlough Hollingshad

Undergraduate Honors Theses

This project focused on ellipsometry, using it to find optical properties of sapphire, and designing a vacuum chamber to expand the temperature range in which we can perform ellipsometry. First, we obtained the anisotropic optical constants of an m-plane sapphire substrate using reflectance ellipsometry and transmission intensity measurements between 0.6 eV and 6.0 eV with a Woollam Inc. variable-angle spectroscopic ellipsometer. These anisotropic optical constants of m-plane sapphire could be used in the future to aid in modeling layered systems where the sapphire is used as a substrate for growing thin film samples of transition metal oxides.

Second ...


Investigating The Use Of Quadrupolar Nuclei For Nmr-Based Quantum Information Processing, Tim W. Milbourne Apr 2014

Investigating The Use Of Quadrupolar Nuclei For Nmr-Based Quantum Information Processing, Tim W. Milbourne

Undergraduate Honors Theses

In this thesis, we apply quantum logic gates to a two-qubit register using the techniques of nuclear magnetic resonance (NMR spectroscopy). We create a lyotropic solution of sodium decyl sulfate (SDS), deuterium oxide (D2O), and decanol in the nematic phase, which functions as our quantum register. Using sequences of single-quantum selective pulses, we generate pseudopure initial states. Using SR, a MatLab-based spin response simulator, we check that the pulse sequences produce the appropriate pseudopure states. We then apply a CNOT quantum logic gate to each initial state. Each pseudopure state reacts as expected to the CNOT gate: while ...


Superconducting Thin Films For Srf Cavity Applications: A Route To Higher Field Gradient Linacs, Wiliam Michael Roach Jan 2014

Superconducting Thin Films For Srf Cavity Applications: A Route To Higher Field Gradient Linacs, Wiliam Michael Roach

Dissertations, Theses, and Masters Projects

Many linear accelerator (linac) applications rely on the use of superconducting radio frequency (SRF) cavities. In order to overcome the current field gradient limits imposed by the use of bulk niobium, a model involving the deposition of alternating superconducting-insulating-superconducting (SIS) thin films onto the interior surface of SRF cavities has been proposed. Since SRF performance is a surface phenomenon, the critical surface of these cavities is less than 1 micron thick, thus enabling the use of thin films. Before such approach can successfully be implemented fundamental studies correlating the microstructure and superconducting properties of thin films are needed. to this ...


Magneto-Optics And Magneto-Transport Studies On Thin Films For Sensor Applications, Kaida Yang Jan 2014

Magneto-Optics And Magneto-Transport Studies On Thin Films For Sensor Applications, Kaida Yang

Dissertations, Theses, and Masters Projects

Recent progress and interest have bought considerable effort to bear on the synthesis and opportunities of magnetic thin films in different fields. There are applications in many fields, including remote sensing, waveguide applications, hard drive applications, etc. at the College of William and Mary, we have focused on utilizing magnetic thin films in some of these applications and are deeply involved in the optimization process of the thin films.


Thermal Tuning Of Mid-Infrared Plasmonic Antenna Arrays Using A Phase Change Material, Mikhail A. Kats, Romain Blanchard, Patrice Genevet, Zheng Yang, Mumtaz M. Qazilbash, D. N. Basov, Shriram Ramanathan, Federico Capasso Jan 2013

Thermal Tuning Of Mid-Infrared Plasmonic Antenna Arrays Using A Phase Change Material, Mikhail A. Kats, Romain Blanchard, Patrice Genevet, Zheng Yang, Mumtaz M. Qazilbash, D. N. Basov, Shriram Ramanathan, Federico Capasso

Arts & Sciences Articles

No abstract provided.


Magnetic Order And Dimensional Crossover In Optical Lattices With Repulsive Interaction, Jie Xu Jan 2013

Magnetic Order And Dimensional Crossover In Optical Lattices With Repulsive Interaction, Jie Xu

Dissertations, Theses, and Masters Projects

One of the most interesting and challenging problems in physics is understanding strongly correlated many-body systems, where strong interactions can yield many remarkable phenomena such as superfluidity in 4He, high-temperature superconductivity, etc. In order to attack these problems, we often need to reduce the complexity of the systems to simple models in hopes of getting better insights into the properties of the systems. The Hubbard model, the focus of this dissertation, is one of the most famous examples of such model, which describes a tunneling of electrons between nearest neighbor sites of a lattice with on-site interactions. This simple model ...


Advanced Topographic Characterization Of Variously Prepared Niobium Surfaces And Linkage To Rf Losses, Chen Xu Jan 2013

Advanced Topographic Characterization Of Variously Prepared Niobium Surfaces And Linkage To Rf Losses, Chen Xu

Dissertations, Theses, and Masters Projects

Superconducting radio frequency (SRF) technology is widely adopted in particle accelerators. The shallow penetration (∼ 40 nm) of the RF into superconducting niobium lends great importance to SRF cavity interior surface chemistry and topography. These in turn are strongly influenced by the chemical etching "surface clean-up" that follows fabrication.;The principal surface smoothing methods are buffered chemical polish (BCP) and electropolish (EP). The resulting topography is characterized by atomic force microscopy (AFM). The power spectral density (PSD) of AFM data provides a more thorough description of the topography than a single-value roughness measurement. In this work, one dimensional average PSD functions ...


Ultra-Thin Perfect Absorber Employing A Tunable Phase Change Material, Mikhail A. Kats, Deepika Sharma, Jiao Lin, Patrice Genevet, Romain Blanchard, Zheng Yang, M. Mumtaz Qazilbash Nov 2012

Ultra-Thin Perfect Absorber Employing A Tunable Phase Change Material, Mikhail A. Kats, Deepika Sharma, Jiao Lin, Patrice Genevet, Romain Blanchard, Zheng Yang, M. Mumtaz Qazilbash

Arts & Sciences Articles

No abstract provided.


Insulator-To-Metal Transition And Correlated Metallic State Of V 2 O 3 Investigated By Optical Spectroscopy, M. K. Stewart, D. Brownstead, S. Wang, K. G. West, J. G. Ramirez, M. Mumtaz Qazilbash, N. B. Perkins, I. K. Schuller, D. N. Basov May 2012

Insulator-To-Metal Transition And Correlated Metallic State Of V 2 O 3 Investigated By Optical Spectroscopy, M. K. Stewart, D. Brownstead, S. Wang, K. G. West, J. G. Ramirez, M. Mumtaz Qazilbash, N. B. Perkins, I. K. Schuller, D. N. Basov

Arts & Sciences Articles

No abstract provided.


First-Principles Calculations Of Nuclear Magnetic Resonance Chemical Shielding Tensors In Complex Ferroelectric Perovskites, Daniel Lawrence Pechkis Jan 2011

First-Principles Calculations Of Nuclear Magnetic Resonance Chemical Shielding Tensors In Complex Ferroelectric Perovskites, Daniel Lawrence Pechkis

Dissertations, Theses, and Masters Projects

Nuclear magnetic resonance (NMR) spectroscopy is one of the most important experimental probes of local atomistic structure, chemical ordering, and dynamics. Recently, NMR has increasingly been used to study complex ferroelectric perovskite alloys, where spectra can be difficult to interpret. First-principles calculations of NMR spectra can greatly assist in this task. In this work, oxygen, titanium, and niobium NMR chemical shielding tensors, s&d4; , were calculated with first-principles methods for ferroelectric transition metal prototypical ABO3 perovskites [SrTiO3, BaTiO 3, PbTiO3 and PbZrO3] and A(B,B')O3 perovskite alloys Pb(Zr1/2Ti1/2)O3 (PZT) and Pb(Mg1/3Nb2/3)O3 ...


Thin Film And Chemical Ordering Effects On The Magnetic Anisotropy In Binary Alloys, Jonathan Ronald Skuza Jan 2011

Thin Film And Chemical Ordering Effects On The Magnetic Anisotropy In Binary Alloys, Jonathan Ronald Skuza

Dissertations, Theses, and Masters Projects

This dissertation presents various investigations into the structure-property correlations in highly anisotropic FePt and FePd thin films and nanostructures. These binary alloy thin films may exhibit long-range chemical ordering (e.g. L10), which induces a strong uniaxial magnetic anisotropy whose orientation is dependent on the ordering direction in the thin film. The chemical ordering, and hence the magnetic anisotropy, in these thin films can be controlled and tailored through sputter deposition and ion implantation conditions followed by subsequent processing. Two novel fabrication methods, x-ray rapid thermal annealing (XRTA) and heavy ion implantation, successfully demonstrate the ability to obtain highly anisotropic ...


Quantum Turbulence In Two Dimensional Bose-Einstein Condensates, Bo Zhang Jan 2011

Quantum Turbulence In Two Dimensional Bose-Einstein Condensates, Bo Zhang

Dissertations, Theses, and Masters Projects

We examine the energy cascades and quantum vortex structures in two-dimensional quantum turbulence through a special unitary time evolution algorithm. An early attempt at using the Lattice Boltzmann Method proved successful in correctly representing some features of the Nonlinear Schrodinger System (NLS), such as the phase shift following the one-dimensional soliton-soliton collision, as well as the two-dimentional modulation instability. However, to accurately evaluate NLS, the implicit Euler method is required to resolve the time evolution, which is computationally expensive. A more accurate and efficient method, the Quantum Lattice Gas model is employed to simulate the quantum turbulence governed by the ...


Enhanced Field Emission From Vertically Oriented Graphene By Thin Solid Film Coatings, Michael Bagge-Hansen Jan 2011

Enhanced Field Emission From Vertically Oriented Graphene By Thin Solid Film Coatings, Michael Bagge-Hansen

Dissertations, Theses, and Masters Projects

Recent progress and a coordinated national research program have brought considerable effort to bear on the synthesis and application of carbon nanostructures for field emission. at the College of William and Mary, we have developed field emission arrays of vertically oriented graphene (carbon nanosheets, CNS) that have demonstrated promising cathode performance, delivering emission current densities up to 2 mA/mm2 and cathode lifetime > 800 hours. The work function ( & phis;) of CNS and other carbonaceous cathode materials has been reported to be &phis;∼4.5-5.1 eV. The application of low work function thin films can achieve several orders of magnitude enhancement of ...


The Functionalization Of Carbon Nanosheets, Ronald A. Quinlan Jan 2009

The Functionalization Of Carbon Nanosheets, Ronald A. Quinlan

Dissertations, Theses, and Masters Projects

Carbon nanosheets are a novel two-dimensional nanostructure made up of 2-20 graphene atomic planes oriented with their in-plane axis perpendicular to the growth substrate. Previous efforts in developing nanosheet technology have focused on the characterization of the system and their development as an electron source due to the high atomic enhancement factor (beta) and low turn on field. Further investigation of nanosheets as high surface area electrodes revealed poor wetting by polymeric material and extreme hydrophobic behavior.;Because nanosheet technology has promise as a high surface area electrode material, this thesis research has focused on three areas of interest: the ...


Correction Of Finite Size Errors In Many-Body Electronic Structure Calculations, Hendra Kwee Jan 2008

Correction Of Finite Size Errors In Many-Body Electronic Structure Calculations, Hendra Kwee

Dissertations, Theses, and Masters Projects

Electronic structure calculations using simulation cells for extended systems typically incorporate periodic boundary conditions as an attempt to mimic the real system with a practically infinite number of particles. Periodic boundary conditions introduce unphysical constraints that give rise to finite-size errors. In mean-field type calculations, the infinite size limit is achieved by simple quadrature in the Brillouin zone using a finite number of k-points. Many-body electronic structure calculations with explicit two-particle interactions cannot avail themselves of this simplification. Direct extrapolation is computationally costly while size correction with less accurate methods is frequently not sufficiently accurate. The Hartree-Fock method neglects the ...


Synthesis And Field Emission Properties Of Carbon Nanostructures, Kun Hou Jan 2008

Synthesis And Field Emission Properties Of Carbon Nanostructures, Kun Hou

Dissertations, Theses, and Masters Projects

This dissertation focuses on developing carbon nanostructures for application as the electron emissive material in novel back-gated triode field emission devices. The synthesis, characterization, and field emission properties of carbon nanostructures, including 1-D carbon nanofibers (CNF), 2-D carbon nanosheets (CNS), and chromium oxide coated carbon nanosheets (CrOx-CNS), are presented in this work.;First, we have fabricated aligned carbon nanofiber based back-gated triode field emission devices and confirmed the operation of these devices. 1-D carbon nanofibers were directly synthesized on blank TiW substrates using direct current plasma enhanced chemical vapor deposition. It was found that the morphology of carbon nanofibers could ...


Magnetization Dynamics And Anisotropy In Ferromagnetic/Antiferromagnetic Ni/Nio Bilayers, Andreas Petersen Jan 2007

Magnetization Dynamics And Anisotropy In Ferromagnetic/Antiferromagnetic Ni/Nio Bilayers, Andreas Petersen

Dissertations, Theses, and Masters Projects

No abstract provided.


First-Principles Calculations Of Electric Field Gradients In Complex Perovskites, Dandan Mao Jan 2007

First-Principles Calculations Of Electric Field Gradients In Complex Perovskites, Dandan Mao

Dissertations, Theses, and Masters Projects

Various experimental and theoretical work indicate that the local structure and chemical ordering play a crucial role in the different physical behaviors of lead-based complex ferroelectrics with the ABO 3 perovskite structure. First-principles linearized augmented plane wave (LAPW) with the local orbital extension method within local density approximation (LDA) are performed on structural models of Pb(Zr1/2Ti1/2 )O3 (PZT), Pb(Sc1/2Ta1/2)O3 (PST), Pb(Sc2/3W1/3)O3 (PSW), and Pb(Mg 1/3Nb2/3)O3 (PMN) to calculate electric field gradients (EFGs). In order to simulate these disordered alloys, various structural models were constructed with ...