Physics Commons^™

Approaching Quantum-Limited Electrometry In The Single-Photon Regime, Sisira Kanhirathingal

Dartmouth College Ph.D Dissertations

Mesoscopic quantum systems currently serve as essential building blocks in many quantum information and metrology devices. This thesis investigates the potential of quantum-limited detection in a mesoscopic electrometer named the cavity-embedded Cooper pair transistor (cCPT). As one application, this charge detector can act as the basis for an optomechanical system in the single-photon strong coupling regime. The realization of this scheme would entail near quantum-limited, ultra-sensitive electrometry at the single-photon level, the feasibility of which is studied at length in this thesis.

On the one hand, we approach this question using a fundamental, first-principles study, where an operator scattering model …

Crystal Growth And Property Tuning Of Layered Magnetic Topological Semimetals, Krishna Pandey

Graduate Theses and Dissertations

The demand for energy-efficient devices has been growing rapidly due to the need for data-driven technologies and the global energy crisis. As device size approaches the atomic scale, the miniaturization of electronic devices may stop in the near future unless fundamentally new materials or device concepts are developed. The emergent topological materials with exotic properties show remarkable robustness against crystal lattice defects, which are promising for next-generation technology. These materials host exotic properties such as high mobility, large magnetoresistance, chiral anomaly, and surface Fermi arcs, etc. Among various topological materials, the ZrSiS-family materials exhibit two types of Dirac states, which …

Tuning Properties Of Topological Insulators: An Ab-Initio Approach, Karunya Shailesh Shirali

LSU Doctoral Dissertations

This thesis develops a first-principles based approach to explore the tuning of topological properties of the tetradymite topological insulators. We begin by setting up a framework to systematically obtain the bulk and surface properties of topological insulators, treating the structural and electronic properties on an equal footing. We determine a consistent method for including the van der Waals interactions, which are responsible for the weak coupling between sets of atomic layers in this family of layered materials, which is important in obtaining accurate structural properties. We obtain close agreement with experimental values for both the bulk and surface states.

To …

Band Structure Topology And Spin Transport In Magnon Systems, Bo Li

Department of Physics and Astronomy: Dissertations, Theses, and Student Research

As the spin excitation quanta in magnetic materials, the magnon is at the heart of the spintronics research because it plays a key role in magnetic dynamics, energy and spin transport, and even determining the ground state of magnetic systems. In this thesis, we will study the band-structure topology and transport properties of magnons in both collinear and noncollinear magnets. Inspired by the great success of topological insulators, exploring magnon topology can unveil the topological nature of bosonic particles and widen the zoo of topological materials. We propose a three-dimensional magnon topological insulator model protected by sublattice chiral symmetries, which …

Superconducting Radio-Frequency Cavity Fault Classification Using Machine Learning At Jefferson Laboratory, Chris Tennant, Adam Carpenter, Tom Powers, Anna Shabalina Solopova, Lasitha Vidyaratne, Khan Iftekharuddin

Electrical & Computer Engineering Faculty Publications

We report on the development of machine learning models for classifying C100 superconducting radio-frequency (SRF) cavity faults in the Continuous Electron Beam Accelerator Facility (CEBAF) at Jefferson Lab. CEBAF is a continuous-wave recirculating linac utilizing 418 SRF cavities to accelerate electrons up to 12 GeV through five passes. Of these, 96 cavities (12 cryomodules) are designed with a digital low-level rf system configured such that a cavity fault triggers waveform recordings of 17 rf signals for each of the eight cavities in the cryomodule. Subject matter experts are able to analyze the collected time-series data and identify which of the …

Memory Formation In Matter, Joseph Paulsen, Nathan C. Keim, Zorana Zeravcic, Srikanth Sastry, Sidney R. Nagel

Physics - All Scholarship

Memory formation in matter is a theme of broad intellectual relevance; it sits at the interdisciplinary crossroads of physics, biology, chemistry, and computer science. Memory connotes the ability to encode, access, and erase signatures of past history in the state of a system. Once the system has completely relaxed to thermal equilibrium, it is no longer able to recall aspects of its evolution. The memory of initial conditions or previous training protocols will be lost. Thus many forms of memory are intrinsically tied to far-from-equilibrium behavior and to transient response to a perturbation. This general behavior arises in diverse contexts …

Gapless Symmetry-Protected Topological Order, Thomas Scaffidi, Daniel E. Parker, Romain Vasseur

Physics Department Faculty Publication Series

We introduce exactly solvable gapless quantum systems in d dimensions that support symmetry-protected topological (SPT) edge modes. Our construction leads to long-range entangled, critical points or phases that can be interpreted as critical condensates of domain walls “decorated” with dimension (d−1) SPT systems. Using a combination of field theory and exact lattice results, we argue that such gapless SPT systems have symmetry-protected topological edge modes that can be either gapless or symmetry broken, leading to unusual surface critical properties. Despite the absence of a bulk gap, these edge modes are robust against arbitrary symmetry-preserving local perturbations near the …

Dynamical Mechanisms Leading To Equilibration In Two-Component Gases, Stephan De Bievre, Carlos Mejia-Monasterio, Paul Ernest Parris

Physics Faculty Research & Creative Works

Demonstrating how microscopic dynamics cause large systems to approach thermal equilibrium remains an elusive, longstanding, and actively pursued goal of statistical mechanics. We identify here a dynamical mechanism for thermalization in a general class of two-component dynamical Lorentz gases and prove that each component, even when maintained in a nonequilibrium state itself, can drive the other to a thermal state with a well-defined effective temperature.

Anisotropic Thermodynamic And Transport Properties Of Single-Crystalline Cakfe4As4, W. R. Meier, T. Kong, U. S. Kaluarachchi, V. Taufour, N. H. Jo, G. Drachuck, A. E. Böhmer, S. M. Saunders, A. Sapkota, A. Kreyssig, M. A. Tanatar, R. Prozorov, A. I. Goldman, Fedor F. Balakirev, Alex Gurevich, S. L. Bud'ko, P. C. Canfield

Physics Faculty Publications

Single-crystalline, single-phase CaKFe₄As₄ has been grown out of a high-temperature, quaternary melt. Temperature-dependent measurements of x-ray diffraction, anisotropic electrical resistivity, elastoresistivity, thermoelectric power, Hall effect, magnetization, and specific heat, combined with field-dependent measurements of electrical resistivity and field and pressure-dependent measurements of magnetization indicate that CaKFe₄As₄ is an ordered, stoichiometric, Fe-based superconductor with a superconducting critical temperature, T_c = 35.0 ± 0.2 K. Other than superconductivity, there is no indication of any other phase transition for 1.8K ≤ T ≤ 300 K. All of these thermodynamic and transport data reveal striking similarities to …

Organic Solar Cells: Electrodes, Performance Enhancement And Degradation Mechanisms, Reginald J. Bauld

Electronic Thesis and Dissertation Repository

In this thesis I focus on a number of aspects associated with the fabrication and characterization of organic photovoltaics. Specifically, my work focuses on evaluating solution processed graphene electrodes for use in organic photovoltaics, improving the performance of indium tin oxide transparent contacts by coating them with Au nanoparticles, and understanding the degradation pathways of Poly(3-hexylthiophene-2,5-diyl): Phenyl-C61-butyric acid methyl ester (P3HT:PCBM) organic solar cells. In my work on graphene electrodes for organic solar cells I worked out a relationship between the sheet resistance and the film transmittance that is useful to optimize such electrodes. Investigation of organic solar cell degradation …

Nonlinear Magnetic Dynamics And The Switching Phase Diagrams In Spintronic Devices, Shu Anthoney Yan

Theses and Dissertations

Spin-transfer torque induced magnetic switching, by which the spin-polarized current transfers its magnetic moment to the ferromagnetic layer and changes its magnetization, holds great promise towards faster and smaller magnetic bits in data-storage applications due to the lower power consumption and better scalability.

We propose an analytic approach which can be used to calculate the switching phase diagram of a nanomagnetic system in the presence of both magnetic field and spin-transfer torque in an exact fashion. This method is applied to the study of switching conditions for the uniaxial, single domain magnetic layers in different spin-transfer devices. In a spin …

Haldane Pseudopotentials And Landau Level Mixing In The Quantum Hall Effect, Rachel Elizabeth Wooten

Doctoral Dissertations

The discovery of the quantum Hall effect in 1980 opened to physics one of the simplest systems for studying many-body correlations. Numerical techniques and trial wavefunctions have proven useful for describing the novel collective behavior of the electrons, but have not fully explained all features of the fractional quantum Hall effect. For example, it is predicted that Landau level mixing should have a moderate effect on the system for all but the very strongest magnetic fields, but this effect has not been extensively studied. Among the tools most useful to modeling and describing the quantum Hall system is the Haldane …

Ab-Initio And Model Studies Of Spin Fluctuation Effects In Transport And Thermodynamics Of Magnetic Metals, James K. Glasbrenner

Department of Physics and Astronomy: Dissertations, Theses, and Student Research

Magnetic materials are vital to many devices and the manipulation of spins is central to the operation of novel devices such as spin transistors. It is important to understand the effect of spin fluctuations on such systems. In this dissertation, first-principles calculations and models further the understanding of spin fluctuation effects in the transport and thermodynamics of magnetic metals.

A simple classical spin-fluctuation Hamiltonian with a single itinerancy parameter is studied using the mean-field approximation, Monte Carlo simulations, and a generalized Onsager cavity field method. The results of these different methods are in agreement. It is found that the thermodynamics …

Superconducting Nafe1-Xcoxas: Crystal Growth, Resistivity, And Susceptibility Measurements, Tucker Netherton

Chancellor’s Honors Program Projects

No abstract provided.

Approach To Accurately Measuring The Speed Of Optical Precursors, Chuan-Feng Li, Zong-Quan Zhou, Heejeong Jeong, Guang-Can Guo

Dartmouth Scholarship

Precursors can serve as a bound on the speed of information with dispersive medium. We propose a method to identify the speed of optical wavefronts using polarization-based interference in a solid-state device, which can bound the accuracy of the speed of wavefronts to less than 10−4 with conventional experimental conditions. Our proposal may have important implications for optical communications and fast information processing.

Design Of Superconducting Multi-Spoke Cavities For High Velocity Applications, C. S. Hopper, Jean R. Delayen

Physics Faculty Publications

Superconducting spoke cavities have been designed and tested for particle velocities up to β₀ ~ 0.6 and are currently being designed for velocities up to β₀ = 1. We present the electromagnetic designs for two-spoke cavities operating at 325 MHz for β₀ = 0.82 and β₀ = 1.

Higher Order Mode Properties Of Superconducting Two-Spoke Cavities, C. S. Hopper, Jean R. Delayen, R. G. Olave

Physics Faculty Publications

Multi-Spoke cavities lack the cylindrical symmetry that many other cavity types have, which leads to a more complex Higher Order Mode (HOM) spectrum. In addition, spoke cavities offer a large velocity acceptance which means we must perform a detailed analysis of the particle velocity dependence for each mode's R/Q. We present here a study of the HOM properties of two-spoke cavities designed for high-velocity applications. Frequencies, R/Q and field profiles of HOMs have been calculated and are reported.

Soliton Stability In A Z (2) Field Theory, J. J. P. Veerman, D. Bazeia, Fernando Moraes

Mathematics and Statistics Faculty Publications and Presentations

We investigate the stability of the coupled soliton solutions of a two-component Z(2) vector fieldmodel, in contraposition to similar solutions of a Z(2)×Z(2)model recently introduced. We demonstrate that the coupled soliton solutions of the Z(2) model are classically unstable.

Peak Effect In Twinned Superconductors, A. I. Larkin, M. Cristina Marchetti, V. M. Vinokur

Physics - All Scholarship

A sharp maximum in the critical current J_c as a function of temperature just below the melting point of the Abrikosov flux lattice has recently been observed in both low and high temperature superconductors. This peak effect is strongest in twinned crystals for fields aligned with the twin planes. We propose that this peak signals the breakdown of the collective pinning regime and the crossover to strong pinning of single vortices on the twin boundaries. This crossover is very sharp and can account for the steep drop of the differential resistivity observed in experiments.

Interface Motion In Random Media At Finite Temperature, Lee-Wen Chen, M. Cristina Marchetti

Physics - All Scholarship

We have studied numerically the dynamics of a driven elastic interface in a random medium, focusing on the thermal rounding of the depinning transition and on the behavior in the

T = 0 pinned phase. Thermal effects are quantitatively more important than expected from simple dimensional estimates. For sufficient low temperature the creep velocity at a driving force equal to the T = 0 depinning force exhibits a power-law dependence on T, in agreement with earlier theoretical and numerical predictions for CDW’s. We have also examined the dynamics in the T = 0 pinned phase resulting from slowly increasing the …

Low-Temperatures Vortex Dynamics In Twinned Superconductors, M. Cristina Marchetti, Valerii M. Vinokur

Physics - All Scholarship

We discuss the low-temperature dynamics of magnetic flux lines in samples with a family of parallel twin planes. A current applied along the twin planes drives flux motion in the direction transverse to the planes and acts like an electric field applied to {\it one-dimensional} carriers in disordered semiconductors. As in flux arrays with columnar pins, there is a regime where the dynamics is dominated by superkink excitations that correspond to Mott variable range hopping (VRH) of carriers. In one dimension, however, rare events, such as large regions void of twin planes, can impede VRH and dominate transport in samples …

Ac Response Of The Flux-Line Liquid In High-Tc Superconductors, Lee-Wen Chen, M. Cristina Marchetti

Physics - All Scholarship

We use a hydrodynamics theory to discuss the response of a viscous flux-line liquid to an ac perturbation applied at the surface of the sample. The theory incorporates viscoelastic effects and describes the crossover between liquid-like and solid-like response of the vortex array as the frequency of the perturbation increases. A large viscosity from flux-line interactions and entanglement leads to viscous screening of surface fields. As a result, two frequency-dependent length scales are needed to describe the penetration of an ac field. For large viscosities the imaginary part of the ac permeability can exihibit, in addition to the well-know peak …

Selective Decay And Coherent Vortices In Two-Dimensional Incompressible Turbulence, William H. Matthaeus, W. Troy Stribling, Daniel Martinez, Sean Oughton, David Montgomery

Dartmouth Scholarship

Numerical solution of two-dimensional incompressible hydrodynamics shows that states of a near-minimal ratio of enstrophy to energy can be attained in times short compared with the flow decay time, confirming the simplest turbulent selective decay conjecture, and suggesting that coherent vortex structures do not terminate nonlinear processes. After all possible vortex mergers occur, the vorticity attains a particlelike character, suggested by the late-time similarity of the streamlines to Ewald potential contours.