Physics Commons^™

Cyclotron Resonance In Graphene Heterostructurescyclotron Resonance In Graphene Heterostructures, Billy Jordan Russell

Arts & Sciences Electronic Theses and Dissertations

We present observations of cyclotron resonance in graphene Van der Waals heterostructure devices. Such devices provide dramatic improvements in sample quality and allow for ad- vanced electronic control, opening windows on previously inaccessible physics. The design and construction of a dedicated system for the measurement of electronic transport and infrared magnetospectroscopy in microscopic samples of atomically thin materials at cryogenic temperatures is presented. In high-mobility encapsulated monolayer graphene, electron- electron interaction effects are unambiguously observed to impact the interband cyclotron resonance as the Landau level filling factor is varied in a quantizing magnetic field. Additionally, a splitting of transitions involving …

Enhanced Magnetic Ordering In Sm Metal And Search For Superconductivity In Cs And Rb Under Extreme Pressure, Yuhang Deng

Arts & Sciences Electronic Theses and Dissertations

At ambient pressure Sm metal orders antiferromagnetically at 106 K and 14 K. The pressure-dependence of the magnetic ordering temperature To of Sm metal was determined through four-point electrical resistivity measurements in a diamond anvil cell to pressures as high as 150 GPa. A strong increase in To with pressure is observed above 85 GPa. In this pressure range Sm ions alloyed in dilute concentration with superconducting Y exhibit giant Kondo pair breaking. Taken together, these results suggest that for pressures above 85 GPa Sm is in a highly correlated electron state, like a Kondo lattice, with an unusually high …

Adiabatic Dark Matter Density Cusps Around Supermassive Black Holes And Dark Matter Detection, Augusto Medeiros Da Rosa

Arts & Sciences Electronic Theses and Dissertations

The growth of a black hole surrounded by dark matter can lead to a significant enhance- ment of the dark matter density close to the hole. We investigate this effect, focusing on the phenomenologically interesting case where the black hole is supermassive and is embedded in a galactic dark matter halo, although the formalism developed does not depend on that fact. Due to the enhanced gravitational potential, the dark matter will tend to cluster around the black hole. The precise details of this clustering will, in general, depend on the formation process of the black hole. However, if the black …

Correlated Sem, Fib, And Tem Studies Of Material Collected By The Nasa Stardust Spacecraft, Brendan Albert Haas

Arts & Sciences Electronic Theses and Dissertations

The objective of this thesis is to describe the study of cometary materials returned by NASA’s Stardust mission. The majority of the research presented in this thesis focuses on improving our characterization and understanding of the fine (< 1 µm) component of comet Wild 2. Investigations of the Stardust foils are conducted with correlated Scanning Electron Microscopy (SEM), Focused Ion Beam (FIB) sample preparation, and Transmission Electron Microscopy (TEM). Investigations of the Stardust aerogels are conducted with plasma ashing sample preparation followed by detailed characterization of the material with TEM. Additional studies of the Stardust interstellar foils, as well as the use of a Convolutional Neural Network (CNN) to search images of the Stardust foils for impact features, are also presented. As a part of this thesis I have developed a new technique for analyzing the Stardust aerogels through the use of plasma ashing sample preparation. This technique is an improvement upon previous attempts to separate cometary materials from the aerogel through the use of HF vapor etching. Plasma ashing allows for cometary materials trapped within the Stardust aerogels to be deposited directly onto TEM grids allowing for detailed characterization of the cometary material with minimal interference from the aerogel itself. The correlated SEM/FIB/TEM studies of the Stardust foils demonstrated here nearly double the number of Stardust craters that have been elementally and structurally characterized in scientific literature. The crater impactor residues were largely composed of combinations of silicates and iron-nickel sulfides that, following impact, rapidly quenched into amorphous melt layers. Two craters were found to contain signatures of the refractory minerals spinel and taenite, indicating a component of the Wild 2 fines originated in the inner Solar System. However, the lack of crystalline material throughout the crater residues suggests that the fine component may largely be composed of amorphous silicates that likely formed in the outer Solar System. Additionally, the submicron Stardust craters appeared enriched in volatile elements relative to CI chondrites, further suggesting that the fine component of Wild 2 originated from a reservoir that was separate from the more refractory coarse (> 1 µm) component. The Stardust aerogel samples returned carbon-rich and potential oldhamite grains. Carbon-rich materials have not been previously observed in the Stardust foils, likely due to the violent collection methods, and the result suggests the ashing technique may be used to better characterize components of the Wild 2 fines that have been difficult to investigate. The presence of oldhamite in the …

Strongly Correlated Systems Under High Magnetic Field: A Mixed Landau Levels Description For Fractional Quantum Hall Effect, Sumanta Bandyopadhyay

Arts & Sciences Electronic Theses and Dissertations

Strong correlation among electrons under high magnetic field gives rise to an entirely new arena of emergent physics, namely fractional quantum Hall effect. Such systems have entirely different elementary degrees of freedom and generally, demand non-perturbative approaches to develop a better understanding. In the literature, there are several analytical methodologies and numerical toolkits available to study such a system. Clustering of zeros, parent Hamiltonian, off-diagonal order parameter, parton construction, matrix product states are to be named among a few of those popular methodologies in the existing literature. Most of these methods work well in the lowest Landau level or holomorphic …

Strongly Correlated Systems Under High Magnetic Field: A Mixed Landau Levels Description For Fractional Quantum Hall Effect, Sumanta Bandyopadhyay

Arts & Sciences Electronic Theses and Dissertations

Strong correlation among electrons under high magnetic field gives rise to an entirely new arena of emergent physics, namely fractional quantum Hall effect. Such systems have entirely different elementary degrees of freedom and generally, demand non-perturbative approaches to develop a better understanding. In the literature, there are several analytical methodologies and numerical toolkits available to study such a system. Clustering of zeros, parent Hamiltonian, off-diagonal order parameter, parton construction, matrix product states are to be named among a few of those popular methodologies in the existing literature. Most of these methods work well in the lowest Landau level or holomorphic …

Electronic Transport Behavior Of Adatom- And Nanoparticle-Decorated Graphene, Jamie Anne Elias

Arts & Sciences Electronic Theses and Dissertations

To induce a non-negligible spin-orbit coupling in monolayer graphene, for the purposes of realizing the Kane-Mele Hamiltonian, transition metal adatoms have been deposited in dilute amounts by thermal evaporation in situ while holding the device temperature near 4K. Electronic transport studies including measurements such as gate voltage dependent conductivity and mobility, weak localization, high field magnetoresistance (Shubnikov de Haas oscillations), quantum Hall, and nonlocal voltage were performed at low temperature before and after sequential evaporations. Studies of tungsten adatoms are consistent with literature regarding other metal adatoms on graphene but were unsuccessful in producing a spin-orbit signature, at least partially …

Extraordinary Magnetoresistance In Encapsulated Graphene Devices, Bowen Zhou

Arts & Sciences Electronic Theses and Dissertations

We report a study on the phenomenon of extraordinary magnetoresistance (EMR) in boron nitride encapsulated monolayer graphene devices. Extremely large EMR values–calculated as the change in magnetoresistance, (R(B)–R0)/R0–can be found in these devices due to the vanishingly small resistance values at zero field. In many devices the zero-field resistance can become negative, which enables R0 to be chosen arbitrarily close to zero depending only on measurement precision, resulting in very large EMR. We critically discuss the dependence of EMR on measurement precision and device asymmetry. On the other hand, we also find the largest reported values of the sensitivity to …

Developing Nucleon Self-Energies To Generate The Ingredients For The Description Of Nuclear Reactions, Mack Charles Atkinson

Arts & Sciences Electronic Theses and Dissertations

The nucleon self-energies of 40Ca, 48Ca, and 208Pb are determined using a

nonlocal dispersive optical model (DOM). By enforcing the dispersion relation

connecting the real and imaginary part of the self-energy, both experimental

scattering data and nuclear structure data are used to constrain these

self-energies. The ability to calculate both bound and scattering states

simultaneously puts these self-energies in a unique position to consistently

describe exclusive knockout reactions such as (e,e'p). Using the

well-constrained self-energy describing 40Ca, the distorted-wave impulse

approximation (DWIA) description of the (e,e'p) reaction is shown to be valid

for outgoing proton kinetic energies around 100 MeV. …

A Test Of The Equivalence Principle Using A Long-Period Torsion Balance, Maneesh Jeyakumar

Arts & Sciences Electronic Theses and Dissertations

The thesis describes an experimental test of Einstein’s Equivalence Principle using a long-period torsion balance. The instrument was operated for a period of ~ 5 months in a remote laboratory at Tyson Research Center. The angular orientation of the balance was recorded with an autocollimating optical lever. Environmental parameters, such as temperature, pressure, and humidity, were also recorded. The thesis focuses on the analysis of this data. Accordingly, novel image processing and tracking algorithms were developed to measure the deflections of the balance over the duration of the experiment. A model of the signal arising from any violation of the …

First-Principles Study Of Structural And Optical Properties Of Novel Materials, Wenshen Song

Arts & Sciences Electronic Theses and Dissertations

Novel materials, including two-dimensional (2D) materials, ferroelectric materials, as well as hybrid perovskites materials, have attracted tremendous attention in recent years because of their unique structural symmetries and electronic structures. Among them, 2D materials, such as graphene, black phosphorene, and transition metal dichalcogenides (TMDs), etc., have great potentials for nanoelectronics and optical applications. Particularly, these 2D materials can sustain much larger strain than their bulk counterparts, making strain a unique and efficient tool to tune a wide range of properties of 2D structures. In the first part of this thesis, we explore how strain tunes quasiparticle energy and excitonic effects …

Exploring Quantum Dynamics And Thermodynamics In Superconducting Qubits, Mahdi Naghiloo

Arts & Sciences Electronic Theses and Dissertations

Quantum technology has been rapidly growing due to its potential revolutionary applications. In particular, superconducting qubits provide a strong light-matter interaction as required for quantum computation and in principle can be scaled up to a high level of complexity. However, obtaining the full benet of quantum mechanics in superconducting circuits requires a deep understanding of quantum physics in such systems in all aspects. One of the most crucial aspects is the concept of measurement and the dynamics of the quantum systems under the measurement process. This thesis is intended to be a pedagogical introduction to the concept of quantum measurement …

Isotopically-Resolved Neutron Cross Sections As Probe Of The Nuclear Optical Potential, Cole Davis Pruitt

Arts & Sciences Electronic Theses and Dissertations

Neutron scattering experiments provide direct access to the forces experienced by nucleons in the nuclear environment. Due to the experimental difficulty of cross section measurements with neutrons, isotopically-resolved neutron scattering cross sections are sorely needed as inputs for many nuclear models. This dissertation presents the results from a campaign of isotope-specific neutron total cross section measurements on 16,18O, 58,64Ni, 112,124Sn, and 103Rh from 3-450 MeV and elastic scattering differential cross section measurements on 112,nat,124Sn at 11 and 17 MeV. Equipped with these new data and with computational improvements to the Dispersive Optical Model (DOM), we present DOM treatments of 16,18O, …