Hydrodynamic Instabilities in Condensed Matter at High Pressures

Dick, Sonya C University of Michigan ProQuest Dissertations & Th 2024 해외박사(DDOD)

소속기관이 구독 중이 아닌 경우 오후 4시부터 익일 오전 9시까지 원문보기가 가능합니다.

The convection of the mantle of Earth and super-Earths is important for many terrestrial phenomena, from plate tectonics to outgassing. Rheological properties, such as viscosity, regulate the transport of thermal energy and mass. However, the viscosity of mantle-relevant materials, such as MgO, at relevant pressures has not been well constrained. The goal of this dissertation is to study hydrodynamic instabilities in condensed matter at high pressures and leverage this understanding to provide a means to measure viscosity at high pressures (100s GPa). Interfacial hydrodynamic instabilities have been widely studied in classical fluid dynamics. Such instabilities occur when perturbations along a material interface are subjected to various processes, including accelerations. The Richtmyer-Meshkov (RM) instability specifically arises when the acceleration is caused by a shock wave. This thesis primarily focuses on the RM instability in condensed matter, which includes solids and liquids subjected to high pressures, i.e., \uD835\uDCAA(106) Pa or greater. Unlike in gases and plasmas, the behavior of the RM instability in condensed matter is highly dependent on viscosity, given the relatively low Reynolds number. As a result, the evolution of the perturbations in such a regime is quite different from that in gases. We are motivated by recent experiments that use hydrodynamic instabilities to infer material properties, such as viscosity, under conditions relevant to planetary interiors and high-pressure environments. There lacks extensive knowledge on the behavior of the Richtmyer-Meshkov instability in condensed matter. We focus on analytically and numerically studying a shocked epoxy-MgO interface, represented by a stiffened equation of state. This thesis presents a comprehensive study of the behavior of condensed matter at shocked interfaces, focusing on both analytical and computational approaches.We first develop an analytical method to determine equation of state parameters in shocked condensed matter for a given interface pressure. By solving an appropriate Riemann problem for the desired pressure, we are able to fit parameters for a stiffened equation of state to experimental data with high accuracy for a number of materials.Next, we explore the Richtmyer-Meshkov instability in condensed matter. The key differences with existing studies RM in gases are that the shocks are far stronger, the sound speeds are larger, and the viscosities are higher. The evolution of a single-mode epoxy-MgO interface is simulated for increasing interface pressures ranging from 50 to 400 GPa. The observed behavior includes dynamic growth rate oscillations and deviations from different growth rate magnitude predictions. The effect of viscosity on this behavior is also probed, and found to decrease the growth rate. The behavior observed in this study is intended to inform the design of experiments in this regime.Finally, we present a numerical investigation of a laser-driven Richtmyer-Meshkov instability accompanying innovative experiments aimed at constraining MgO viscosity. This work establishes a robust platform that incorporates the dynamic OMEGA-EP laser, the experimentally relevant equations of state for each material, and the constitutive relations of shocked condensed matter. Simulations are performed for a variety of different MgO viscosities in order to constrain the experimental data. The early-time evolution of the simulations, when compared to the experimental data, suggest the viscosity of MgO at these conditions is within an order of magnitude of 5000 Pa·s. These multi-physics simulations are necessary and critical to constrain the viscosity in this campaign. We further investigate the strain rate dependence of viscosity. By accounting for the expected decrease in viscosity at the shock front and rarefaction, better agreement between the simulations and the experimental data is achieved, thus providing a characterization of the rate dependence of viscosity.

Hollow Condensates, Topological Ladders and Quasiperiodic Chains

Padavic-Callaghan, Karmela ProQuest Dissertations & Theses University of Illi 2020 해외박사(DDOD)

소속기관이 구독 중이 아닌 경우 오후 4시부터 익일 오전 9시까지 원문보기가 가능합니다.

This thesis presents three distinct topics pertaining to the intersection of condensed matter and atomic, molecular and optical (AMO) physics. We theoretically address the physics of hollow Bose-Einstein condensates and the behavior of vortices within them then discuss localization-delocalization physics of one-dimensional quasiperiodic models, and end by focusing on the physics of localized edge modes and topological phases in quasi-one-dimensional ladder models. For all three topics we maintain a focus on experimentally accessible, physically realistic systems and explicitly discuss experimental implementations of our work or its implications for future experiments. First, we study shell-shaped Bose-Einstein condensates (BECs). This work is motivated by experiments aboard the International Space Station (ISS) in the Cold Atom Laboratory (CAL) where hollow condensates are being engineered. Additionally, shell-like structures of superfluids form in interiors of neutron stars and with ultracold bosons in three-dimensional optical lattices. Our work serves as a theoretical parallel to CAL studies and a step towards understanding these more complex systems. We model hollow BECs as confined by a trapping potential that allows for transitions between fully-filled and hollow geometries. Our study is the first to consider such a real-space topological transition. We find that collective mode frequencies of spherically symmetric condensates show non-monotonic features at the hollowing-out point. We further determine that for fully hollow spherically symmetric BECs effects of Earth's gravity are very destructive and consequently focus on microgravity environments. Finally, we study quantized vortices on hollow condensate shells and their response to system rotation. Vortex behavior interesting as a building block for studies of more complicated quantum fluid equilibration processes and physics of rotating neutron stars interiors. Condensate shells' closed and hollow geometry constrains possible vortex configurations. We find that those configurations are stable only for high rotation rates. Further, we determine that vortex lines nucleate at lower rotation rates for hollow condensates than those that are fully-filled.Second, we analyze the effects of quasiperiodicity in one-dimensional systems. Distinct from truly disordered systems, these models exhibit delocalization in contrast to well-known facts about Anderson localization. We study the famous Aubry-Andre-Harper (AAH) model, a one-dimensional tight-binding model that localizes only for sufficiently strong quasiperiodic on-site modulation and is equivalent to the Hofstadter problem at its critical point. Generalizations of the AAH modelhave been studied numerically and a generalized self-dual AAH model has been proposed and analytically analyzed by S. Ganeshan, J. Pixley and S. Das Sarma (GPD). For extended and generalized AAH models the appearance of a mobility edge i.e. an energy cut-off dictating which wavefunctions undergo the localization-delocalization transition is expected. For the GPD model this critical energy has been theoretically determined. We employ transfer matrices to study one-dimensional quasiperiodic systems. Transfer matrices characterize localization physics through Lyapunov exponents. The symplectic nature of transfer matrices allows us to represent them as points on a torus. We then obtain information about wavefunctions of the system by studying toroidal curves corresponding to transfer matrix products. Toroidal curves for localized, delocalized and critical wavefunctions are distinct, demonstrating a geometrical characterization of localization physics. Applying the transfer matrix method to AAH-like models, we formulate a geometrical picture that captures the emergence of the mobility edge. Additionally, we connect with experimental findings concerning a realization of the GPD model in an interacting ultracold atomic system.Third, we consider a generalization of the Su-Schrieffer-Heeger (SSH) model. The SSH chain is a one-dimensional tight-binding model that can host localized bound states at its ends. It is celebrated as the simplest model having topological properties captured by invariants calculated from its band-structure. We study two coupled SSH chains i.e. the SSH ladder. The SSH ladder has a complex phase diagram determined by inter-chain and intra-chain couplings. We find three distinct phases: a topological phase hosting localized zero energy modes, a topologically trivial phase having no edge modes and a phase akin to a weak topological insulator where edge modes are not robust. The topological phase of the SSH ladder is analogous to the Kitaev chain, which is known to support localized Majorana fermion end modes. Bound states of the SSH ladder having the same spatial wavefunction profiles as these Majorana end modes are Dirac fermions or bosons. The SSH ladder is consequently more suited for experimental observation than the Kitaev chain. For quasiperiodic variations of the inter-chain coupling, the SSH ladder topological phase diagram reproduces Hofstadter's butterfly pattern. This system is thus a candidate for experimental observation of the famous fractal. We discuss one possible experimental setup for realizing the SSH ladder in its Kitaev chain-like phase in a mechanical meta-material system. This approach could also be used to experimentally study the Hofstadter butterfly in the future.Presented together, these three topics illustrate the richness of the intersection of condensed matter and AMO physics and the many exciting prospects of theoretical work in the realm of the former combining with experimental advances within the latter.

응집물질물리분야 연구데이터 관리 방안 연구

김성욱 전북대학교 일반대학원 2020 국내석사

In this study, we proposed a method to systematically manage research data in the field of condensed matter physics, which is the most active and interdisciplinary field. In the course of the research, a questionnaire was conducted for researchers in the field of condensed matter physics. The questionnaire was constructed based on the research data management tool Data Asset Framework(DAF) and the FAIR principle for data sharing and reuse. The current status of research data management in the field of condensed matter physics was collected from 14 researchers. The collected data consisted of data on the characteristics and basic information of researchers who answered the questionnaire, data preservation and management, and data sharing and access. By analyzing the collected questionnaire results, nine problems were drawn about the characteristics of research data in the field of condensed matter physics, data collection and production, data preservation and management, data sharing and access. In terms of data collection and production, the lack of a management system reflecting the experimental process, lack of guidelines for various types of research data, and a lack of a management system reflecting the sensitivity and confidentiality of research data were identified as problems. In terms of data preservation and management, the lack of formal data management plans and guidelines/policies, lack of responsibility for researchers, research data management gap, and loss of research data were identified as problems. In terms of data sharing and access, the limitations of the sharing and access of research data and the lack of a system for accessing and reusing data were drawn as problems. In this study, suggestions were made to improve the problems derived from each aspect.

From Fractons to Fractional Hall: An Exploration of Exotic Quantum Field Theories

Raz, Amir The University of Texas at Austin ProQuest Dissert 2025 해외박사(DDOD)

소속기관이 구독 중이 아닌 경우 오후 4시부터 익일 오전 9시까지 원문보기가 가능합니다.

Quantum field theory remains at the epicenter of both theoretical high energy and condensed matter physics. Given this, it is quite surprising that many diverse systems at very different scales can be studied using the same tools of quantum field theory. While quantum field theory has been incredibly successful in describing many universal properties of condensed matter systems as well as the standard model of particle physics, there are still many systems and phenomena that are difficult to study using conventional quantum field theory techniques. This is either because such systems don't seem to nicely fit into the standard paradigms of quantum field theory, or because the coupling between the various constituents is strong and so the conventional perturbative methods break down. This thesis focuses on two such systems from arising from the study condensed matter, fractonic systems and the fractional quantum Hall effect; with two overarching goals: trying to understand exactly how these exotic condensed matter systems fit into (or expand) the paradigms of quantum field theory, and adapting techniques developed in the high energy community to investigate strongly interacting systems in condensed matter.

Coulomb correlations in equilibrium and nonequilibrium many-fermion systems

Setlur, Girish Sampath University of Illinois at Urbana-Champaign 1999 해외박사(DDOD)

소속기관이 구독 중이 아닌 경우 오후 4시부터 익일 오전 9시까지 원문보기가 가능합니다.

The importance of the field of Condensed Matter Physics can hardly be overstated. It deals with matter at everyday energies and with length and times scales in which complex processes are able to occur. It is a field in which much experimental and theoretical effort has been invested. New experimental techniques continue to shift the boundaries of this diverse field. Yet the theoretical tools that have been brought to bear on these problems have had a distinctly stale flavor. Only recently have theorists woken up to the possibility that modern techniques developed mainly by particle theorists could be fruitfully applied to study these problems. The aim of this thesis is therefore to study important physical phenomena in Condensed Matter Physics using tools that are powerful enough to be able to probe new physics. In the first part of this thesis I have shown how transient Many-Body phenomena may be studied using nonequilibrium Green functions. In the second half I have developed a new nonpertubative tool called bosonization and applied it to study the all-important question at the frontier of Condensed Matter Theory namely when does Fermi liquid theory break down and when it does what new physical principles need to be invoked in order to understand physical phenomena in this new and uncharted regime.

Dark Matter Couture: Designer Targets and Tailored Detectors for Next-Generation Searches

Ashour, Omar A University of California, Berkeley ProQuest Disser 2025 해외박사(DDOD)

소속기관이 구독 중이 아닌 경우 오후 4시부터 익일 오전 9시까지 원문보기가 가능합니다.

Despite sustained efforts, direct detection of dark matter (DM) remains elusive. Propelled by cutting-edge advances in detector sensitivity and innovative proposals employing quantum materials, the search for DM has recently expanded to lower masses, encompassing well-motivated theories for light and ultralight candidates. However, detecting these low-mass candidates remains a formidable challenge, requiring target materials that exhibit measurable responses with just a few meV of energy deposition from dark matter scattering or absorption.State-of-the-art approaches for light DM detection face several challenges, including low-energy background discrimination, detection of single-phonons and single-magnons, and losses at the target-sensor interface. We address these challenges by proposing novel and complementary strategies from condensed matter physics: pressure-tunable targets and topological transition sensors.The first Chapter of this Dissertation provides a broad overview of DM and the effective field theory (EFT) we use to compute DM scattering rates from collective excitations in condensed matter systems. The second Chapter introduces relevant concepts from condensed matter theory, including the foundations of phonons and magnons within both classical and quantum formalisms. We detail several approaches for computing phonons and magnons from first-principles density functional theory (DFT), and close the Chapter by introducing topological insulators, a class of quantum materials central to most of the work we present.In the third Chapter, we explore how hydrostatic pressure---a well-established tool for tuning properties of condensed matter---presents a novel route for optimizing targets for light dark matter direct detection, specifically via phonons. Highly compressible solids are profoundly affected by pressure, and our results show that, in solid helium, the speed of sound and phonon frequencies are significantly enhanced by applying pressures up to 40 GPa. Our ab initio calculations illustrate how high pressure elevates helium from lacking single-phonon reach to rivaling leading candidates. Our findings establish pressure as an unexplored tuning knob for accessing lower dark matter mass regimes and suggest potential new avenues for background discrimination.In the fourth Chapter, we introduce topological transition sensors (TTSs), novel quantum sensors based on the bulk-boundary correspondence of topological insulators. Here, our DFT calculations show how phonons and magnons can transiently break bulk symmetries, gapping out topological surface states and driving a metal-insulator transition on the material's surface. We elucidate the unique advantages of TTSs for light DM detection and quantum sensing that complement conventional state-of-the-art cryogenic sensors. Further, we explore several readout schemes, and highlight the distinctive properties of TTSs, including directionality and quasiparticle selectivity.The fifth and sixth Chapters delve deeper into material realizations of TTSs in topological crystalline insulators (TCIs) for phonons and antiferromagnetic topological insulators (AFTIs) for magnons. We highlight the essential material properties for ideal TTS candidates, and thoroughly examine two material candidates, namely TCI Sr3PbO for phonons and AFTI VBi2Te2Se2 for magnons. These Chapters highlight many of the unique properties of TTSs that arise as a direct consequence of the interplay between the symmetries protecting the bulk topology and the quasiparticle-induced transient symmetry breaking. Further, we explore the inherent directionality of TTSs and illustrate the potential of doubly-topological materials for correlated multichannel sensing. Finally, in the seventh Chapter, we summarize our findings and explore future directions for tunable detectors and TTSs.

Applications of holography to condensed-matter physics

Thompson, Ethan Greene University of Washington 2010 해외박사(DDOD)

소속기관이 구독 중이 아닌 경우 오후 4시부터 익일 오전 9시까지 원문보기가 가능합니다.

Holography is perhaps the most powerful tool we have to investigate strongly-coupled field theories. In recent years, it has begun to find application to problems in condensed-matter physics. In this thesis, we review a number of such applications and the general state of the field.

On the electronic and magnetic properties of nanostructures, solids and cold atomic gases

Sau, Jay Deep University of California, Berkeley 2008 해외박사(DDOD)

소속기관이 구독 중이 아닌 경우 오후 4시부터 익일 오전 9시까지 원문보기가 가능합니다.

In this work we calculate the properties of several condensed matter systems using a combination of empirical model Hamiltonian approaches and methods from computational condensed matter physics such as density functional theory and numerical solutions of the mean-field Gross-Pitaevskii equations. This work has been organized into 7 chapters as follows. (1) In the first chapter we motivate the discussion for the rest of the thesis and discuss the theoretical ideas that underly the work. (2) In the second chapter we discuss the approaches and approximations such as density functional theory and many-body perturbation theory that have been used in this research to make the many-electron problem a tractable one. (3) In the third chapter we discuss the application of density functional theory calculations to the analysis of scanning tunneling microscope (STM) images of boron nitride nanotubes. It is found experimentally and confirmed theoretically that the electric field of the STM can be used to lower the gap of the nanotube in a controllable fashion and also the modify the shape of the electronic states on the nanotube. (4) In the fourth chapter we extend the idea of modifying electronic properties of boron nitride nanotubes with an STM and apply the principle to carbon nanotube bundles. In this study a combination of density functional theory and model Hamiltonian calculations is used to derive a theoretical prediction where the application of an electric field through an STM can drive a transition of a nanotube bundle from a semiconductor to an excitonic system where the ground state is populated with a density of excitons that is tunable by the electric field strength. (5) In the fifth chapter we discuss another class of nanosystems, and focus on molecules on metallic substrates. These systems have been the subject of a large number of studies because of their technological relevance to solar-cells and molecular electronic devices. In this chapter we develop a technique to determine the level alignment and gaps of a molecule in the neighborhood of a substrate. We then test our method by quantitatively comparing the results of this method applied to the C 60 molecule on Au and Ag substrates to experimental scanning tunneling spectroscopy results on these systems. (6) In chapter six we move our focus to bulk systems and use a combination of density functional theory and empirical pseudopotential methods to study the transport properties of Ge-Sn alloy systems. Using the empirical pseudopotential method we find a combination of strain and alloying that turns Ge-Sn into a direct gap semiconductor with low electron and hole masses. The low effective masses implies an increased carrier mobility for the alloy. Using density functional theory calculations we calculate the effect of alloy scattering from Sn in Ge and show that even after taking into account substitutional disorder from alloy scattering Ge-Sn alloys are expected to exhibit higher mobilities than Ge. (7) In the final chapter we apply the combination of a model Hamiltonian and a computational solution of mean field equations that we have been applying to solid state systems to understand and predict the properties of ultra-cold spinor Bose Eintein Condensates. In this study we study the effect of how dipole-dipole interactions between spin-1 Rubidium atoms can directly affect the dynamics of quantum noise induced domain formation and predict ways to directly observe the dipole-dipole interactions between 87Rb.

Superconductivity and ferromagnetism in topological insulators

Zhang, Duming The Pennsylvania State University 2012 해외박사(DDOD)

소속기관이 구독 중이 아닌 경우 오후 4시부터 익일 오전 9시까지 원문보기가 가능합니다.

Topological insulators, a new state of matter discovered recently, have attracted great interest due to their novel properties. They are insulating inside the bulk, but conducting at the surface or edges. This peculiar behavior is characterized by an insulating bulk energy gap and gapless surface or edge states, which originate from strong spin-orbit coupling and time-reversal symmetry. The spin and momentum locked surface states not only provide a model system to study fundamental physics, but can also lead to applications in spintronics and dissipationless electronics. While topological insulators are interesting by themselves, more exotic behaviors are predicted when an energy gap is induced at the surface. This dissertation explores two types of surface state gap in topological insulators, a superconducting gap induced by proximity effect and a magnetic gap induced by chemical doping. The first three chapters provide introductory theory and experimental details of my research. Chapter 1 provides a brief introduction to the theoretical background of topological insulators. Chapter 2 is dedicated to material synthesis principles and techniques. I will focus on two major synthesis methods: molecular beam epitaxy for the growth of Bi₂Se₃ thin films and chemical vapor deposition for the growth of Bi₂Se₃ nanoribbons and nanowires. Material characterization is discussed in Chapter 3. I will describe structural, morphological, magnetic, electrical, and electronic characterization techniques used to study topological insulators. Chapter 4 discusses the experiments on proximity-induced superconductivity in topological insulator (Bi₂Se₃) nanoribbons. This work is motivated by the search for the elusive Majorana fermions, which act as their own antiparticles. They were proposed by Ettore Majorara in 1937, but have remained undiscovered. Recently, Majorana's concept has been revived in condensed matter physics: a condensed matter analog of Majorana fermions is predicted to exist when topological insulators are interfaced with superconductors. The observation of Majorana fermions would not only be fundamentally important, but would also lead to applications in fault-tolerant topological quantum computation. By interfacing topological insulator nanoribbons with superconducting electrodes, we observe distinct signatures of proximity-induced superconductivity, which is found to be present in devices with channel lengths that are much longer than the normal transport characteristic lengths. This might suggest preferential coupling of the proximity effect to a ballistic surface channel of the topological insulator. In addition, when the electrodes are in the superconducting state, we observe periodic magnetoresistance oscillations which suggest the formation of vortices in the proximity-induced region of the nanoribbons. Our results demonstrate that proximity-induced superconductivity and vortices can be realized in our nanoribbon geometry, which accomplishes a first important step towards the search for Majorana fermions in condensed matter. In Chapter 5, I will discuss experiments on a magnetically-doped topological insulator (Mn-doped Bi₂Se₃) to induce a surface state gap. The metallic Dirac cone surface states of a topological insulator are expected to be protected against small perturbations by time-reversal symmetry. However, these surface states can be dramatically modified and a finite energy gap can be opened at the Dirac point by breaking the time-reversal symmetry via magnetic doping. The interplay between magnetism and topological surface states is predicted to yield novel phenomena of fundamental interest such as a topological magneto-electric effect, a quantized anomalous Hall effect, and the induction of magnetic monopoles. Our systematic measurements reveal a close correlation between the onset of ferromagnetism and quantum corrections to diffusive transport, which crosses over from the symplectic (weak anti-localization) to the unitary (weak localization) class. A comprehensive interpretation of data obtained from electrical transport, angle-resolved photoemission spectroscopy, superconducting quantum interference device magnetometry, and scanning tunneling microscopy indicates that the ferromagnetism responsible for modifications in the surface states occurs in nanoscale regions on the surface where magnetic atoms segregate during sample growth. This suggests that some aspects of the observed magnetoconductance may indeed originate from surface transport despite the non-ideal nature of the samples. These observations are consistent with the prediction of a time-reversal symmetry breaking gap, which is further supported by angle-resolved photoemission spectroscopy measurements.

Rabi splitting enhancement in semiconductor microcavities

Dickerson, James Henry, II State University of New York at Stony Brook 2002 해외박사(DDOD)

소속기관이 구독 중이 아닌 경우 오후 4시부터 익일 오전 9시까지 원문보기가 가능합니다.

The physics of the two-level atom has been the basis of research in atomic physics for much of the past several decades. One of the great successes of semiconductor physics has been its capability to mimic the phenomena of other physical systems. Many of the discoveries in atomic physics have prompted studies of the coupling between two-level atom-like structures and photonic system in semiconductor physics. Much of that work has investigated the optics of the energy exchange between atom-like systems and the electromagnetic field mode of the enclosing cavity. Since many applications of microcavities are governed by the control of the spontaneous emission from the structure, command of the emission relies on control of the coupling between the photonic and the excitonic modes of the system. When the energies of the interacting microcavity states are in resonance, the resulting degeneracy yields an energy split between the coincident modes. This energy split produces two branches of the resonant mixed states, which are called polaritons. The energy separation between the mixed state branches is called the vacuum Rabi splitting, Δ. The magnitude of the Rabi splitting is indicative of the coupling strength of the polariton modes. One of the major pursuits of this field has been to augment the control of the coupling strength between the cavity polariton modes. Comprehensive control over the polariton states, be it the modulation of the polariton energies or the suppression of one of the modes, is a key component in the development of microcavity devices. The goal of my thesis research was to discover a simple means to achieve control over the coupling between the photonic and excitonic modes of a microcavity. This entailed the parametric tuning of the Rabi splitting between the coupled modes of the microcavity. Furthermore, we hoped to attain the maximum possible Rabi splitting observed in GaAs/Al<italic>_x</italic>Ga₁₋<italic>_x</italic>As microcavities with quantum oscillators located only within the cavity region.