Condensed Matter Physics Commons^™

Glassy Magnetic Freezing Of Interacting Clusters In Materials Related To The Lk-99 Family, Serafim Teknowijoyo, Domenico Napoletani, Vahan Nikoghosyan, Armen Gulian

Mathematics, Physics, and Computer Science Faculty Articles and Research

We report reproducible magnetization anomalies appearing below room temperature in copper-doped apatite materials belonging to the LK-99 family synthesized via hydrothermal methods. These anomalies are observed consistently across samples prepared under comparable conditions. Although the extracted Mydosh parameter lies within the range often associated with vortex-glass behavior in superconductors, a detailed analysis of DC magnetization, AC susceptibility, field dependence, and magnetic memory effects demonstrates that the observed phenomena are not related to superconductivity. Instead, the data are consistent with glassy magnetic freezing of interacting clusters. Compositional and structural analysis identifies covellite (CuS), one of the constituent phases in these multiphase …

Electronic Transport In Twisted Bilayer Tungsten Diselenides, Walid Zaher

Theses and Dissertations

This thesis investigates density waves (DWs) in twisted bilayer tungsten diselenide (tWSe₂) using a mean field approximation, with a focus on electron-electron interactions, and the system’s free energy at zero temperature. For the mean field approximation, the study initially employed same-spin nesting vectors, which were found insufficient to induce DWs formation. In contrast, when opposite-spin nesting vectors were used, DWs emerged, indicating that these vectors can support DWs formation. The plots were produced under perfect nesting conditions, where van Hove singularities (VHS) occur. At zero temperature, perfect nesting provides a complete picture of the upper limit of DWs formation, as …

First Principles Calculation Of Electron-Phonon Coupling In Nonequilibrium Quantum Materials, Chendi Xie

All Dissertations

This dissertation combines first-principles computation and light-induced nonequilibrium analysis to understand and control electron–phonon coupling (EPC) and emergent many-body phenomena in quantum materials, in both equilibrium and nonequilibrium states.

Chapters 1 and 2 build the theoretical and computational foundation, beginning with electron and phonon self-energies, linewidths, and perturbation theory for EPC, followed by density functional theory (DFT) and density functional perturbation theory (DFPT), which serve as the first-principles workhorses used throughout. Chapter 3 reviews Bardeen-Cooper-Schrieffer (BCS) and Migdal-Eliashberg theory, including the BCS gap - transition temperature (T_c) relation and the strong-coupling generalization, and delineates the practical validity bound …

Gate-Controlled Supercurrent Effect In Dry-Etched Dayem Bridges Of Non-Centrosymmetric Niobium Rhenium, Jennifer Koch, Carla Cirillo, Sebastiano Battisti, Leon Ruf, Zahra Makhdoumi Kakhaki, Alessandro Paghi, Armen Gulian, Serafim Teknowijoyo, Giorgio De Simoni, Francesco Giazotto, Carmine Attanasio, Elke Scheer, Angelo Di Bernardo

Mathematics, Physics, and Computer Science Faculty Articles and Research

The application of a gate voltage to control the superconducting current flowing through a nanoscale superconducting constriction, named as gate-controlled supercurrent (GCS), has raised great interest for fundamental and technological reasons. To gain a deeper understanding of this effect and develop superconducting technologies based on it, the material and physical parameters crucial for the GCS effect must be identified. Top-down fabrication protocols should also be optimized to increase device scalability, although studies suggest that top-down fabricated devices are more resilient to show a GCS. Here, we investigate gated superconducting nanobridges made with a top-down fabrication process from thin films of …

Design And Performance Of Superconducting Switches For Nanowire Detectors In Magnetic Fields, Timothy James Draher

Graduate Research Theses & Dissertations

Superconducting nanowire devices fit a broad spectrum of applications, including particle detection and quantum computing, and their expanding use across various fields highlights their role in the hybridization of superconducting and conventional semiconductor electronics. Despite their potential, the low signal output of these devices raises challenges in scalability and integration, particularly in applications for nuclear and high-energy physics, where resilience in magnetic fields is becoming a critical optimization factor. The superconducting nanowire cryotron (nTron) addresses these issues by providing operational gain and logic switching in superconducting nanowire circuits, demonstrating adaptability to multiple materials. This dissertation focuses on modifying the conventional …

Computational Modeling Of Superconductivity From The Set Of Time-Dependent Ginzburg-Landau Equations For Advancements In Theory And Applications, Iris Mowgood

Computational and Data Sciences (PhD) Dissertations

A full review of the research conducted and published during my PhD studies in Computational and Data Sciences at Chapman University, under the advisement of Dr. Armen Gulian, are presented. Using the set of time-dependent Ginzburg-Landau (TDGL) equations with inclusion of the interference current and the non-equilibrium phonon term, we modeled the dynamics of superconductors in various theory revealing states and practical purposes. A review of the history and phenomenon of superconductivity, including modern applications, is introduced. The Josephson effect and associated Josephson junction are discussed for comparison to our analogous results with the 1-D superconducting wire. The mathematics of …

Stoichiometric Determination Of Hydride Materials At Extreme Conditions, Gregory Alexander Smith

UNLV Theses, Dissertations, Professional Papers, and Capstones

Hydrogen was predicted to be a high-temperature superconductor at near-megabar conditions in 1968,[1] but only recently was been experimentally observed.[2] This is due to the extraneous metrological constraint of requiring 5 megabars of pressure to stabilize. A more practical approach for synthesis of high-temperature superconductors has been pro-posed through the use of hydride compounds. Recently, a surge of rare earth hydrides have achieved critical superconducting transition temperatures (T_C ) close to room temperature.[3, 4, 5, 6] However, due to limitations of the necessary instrumentation to achieve megabar pressures, many techniques traditionally used to measure stoichiometry are unavailable.Three works presented in …

Novel Low Temperature Properties Of Filled And Unfilled Single Crystal Irsb3, Matthew Cook

Dissertations

The skutterudite family of materials has garnered a lot of attention in the condensed matter community and it persists to be an important system for exploring the fundamental physics of solids. The initial interest into compounds with this common structure was due to their promising thermoelectric properties giving the possibility of efficient energy harvesting. Since, there has been a huge effort to systematically synthesize new filled skutterudite compounds, as nearly every type of strongly correlated behavior has been found within this family. As the field of topological materials has gained momentum, these materials have also been given a renewed interest …

Majorana Quasiparticles In Topological Material Interfaces, David Alspaugh

LSU Doctoral Dissertations

In this dissertation we analyze how Majorana quasiparticles found on material interfaces of both topological insulators (TIs) and topological superconductors (TSCs) are affected by imperfections within their local environment. While these quasiparticles are predicted to be critical for the construction of quantum computers, they are typically modeled only under pristine conditions. Thus, although quantum computers may require the spatial manipulation of Majorana quasiparticles, these topological material interfaces are commonly studied in static contexts and their response to manipulation remains an open question. We first demonstrate that interface potentials on the topological insulator Bi₂Se₃ can enable the emergence …

Experimental Exploration Of Shared Magnetic Phases Between Diverse Systems Of Iron-Pnictide Superconductors, Ryan Scott Stadel

Graduate Research Theses & Dissertations

The exciting field of iron-pnictide superconductors offers unique opportunities for studying the relationship between magnetism and unconventional superconductivity. This is vital to developing an understanding of the microscopic origin of high-temperature superconductivity, which is itself an important step in harnessing such a potentially revolutionary technology.

Polycrystalline and crystalline samples are synthesized over a diverse collection of related iron-pnictide systems including (Ca,Sr,Ba)1-xNaxFe2As2, Ba(Fe1-xCox)2As2 (122s), and LaFeAs1-xPxO, and TbFeAs1-xPxO (1111s). These compounds are characterized through various types of neutron and x-ray diffraction on multiple instruments, as well as muon spin resonance, and magnetic susceptibility measurements.

A thorough investigation into the conditions under …

Superconducting Phase Transition In Inhomogeneous Chains Of Superconducting Islands, Eduard Ilin, Irina Burkova, Xiangyu Song, Michael V. Pak, Dmitri S. Golubev, Alexey Bezryadin

Faculty Publications

We study one-dimensional chains of superconducting islands with a particular emphasis on the regime in which every second island is switched into its normal state, thus forming a superconductor-insulator-normal metal (S-I-N) repetition pattern. As is known since Giaever tunneling experiments, tunneling charge transport between a superconductor and a normal metal becomes exponentially suppressed, and zero-bias resistance diverges, as the temperature is reduced and the energy gap of the superconductor grows larger than the thermal energy. Here we demonstrate that this physical phenomenon strongly impacts transport properties of inhomogeneous superconductors made of weakly coupled islands with fluctuating values of the critical …

The Synthesis Of Pb2sr2sm1-Xcaxcu3o8 And Characterization Of Its Structural And Superconducting Properties., Deblina Das

Graduate Research Theses & Dissertations

Superconducting lead-based cuprate materials of the 2213 structural type, Pb2Sr2MCu3O8 (M=Sm1-xCax, Y1-xCax, Er1-xCax and Yb1-xCax), were synthesized and characterized using x-ray powder diffraction and the Rietveld structural refinements method. Pb2Sr2Sm1-xCaxCu3O8 single crystals were grown by an optimized flux method using various combinations of PbO/PbF2 solvents. Samples with different Sm/Ca ratios were investigated for their superconducting properties. Magnetic measurements reveal the presence of a transition at 120K. Preliminary x-ray diffuse scattering experiment at the Advanced Photon Source of Argonne National Laboratory demonstrates the high quality of one of our crystals and the presence of rod-like diffuse scattering connecting the Bragg peaks …

Non-Centrosymmetric Superconductivity And Magnetism In The Presence Of Broken Symmetries, Mojammel Alam Khan

LSU Doctoral Dissertations

Non-centrosymmetric (NC) superconducting and magnetic compounds have been synthesized and investigated using magnetic, specific heat, and transport measurements, as well as by neutron scattering and quantum oscillations. The crystal structures of NC compounds are defined by the lack of an inversion center. In NC superconductors, a finite antisymmetric spin orbit coupling originating from broken inversion symmetry results in unconventional Cooper pairing. Instead of a single spin channel, the order parameter is a mixture of spin-singlet and spin-triplet states. For NC magnetic compounds, the antisymmetric and isotropic spin interactions compete, leading to a helical ground state.

We have studied the NC …

Nonlinear Dynamics Of Vortices In Different Types Of Grain Boundaries, Ahmad K. Sheikhzada

Physics Theses & Dissertations

As a major component of linear particle accelerators, superconducting radio-frequency (SRF) resonator cavities are required to operate with lowest energy dissipation and highest accelerating gradient. SRF cavities are made of polycrystalline materials in which grain boundaries can limit maximum RF currents and produce additional power dissipation sources due to local penetration of Josephson vortices. The essential physics of vortex penetration and mechanisms of dissipation of vortices driven by strong RF currents along networks of grain boundaries and their contribution to the residual surface resistance have not been well understood. To evaluate how GBs can limit the performance of SRF materials, …

Power Distribution Of Terahertz Emission From Hexagonal Bscco Microstrip Antennas, Andrew E. Davis

Honors Undergraduate Theses

We analyze the distribution of coherent terahertz radiation from a regular hexagonal microstrip antenna (MSA) made from the high-T_c superconductor Bi₂Sr₂CaCu₂O_8+x (BSCCO). We discuss the C_6v symmetry of the solutions of the wave equation on a hexagonal domain and distinguish between the closed-form and non-closed-form solutions. The closed-form wavefunctions of the transverse magnetic (TM) electromagnetic cavity modes are presented and formulas for the radiated power arising from the uniform part of the AC Josephson current and from the resonant cavity modes are derived. The wavefunctions and angular distribution of radiation from …

The Effect Of Impurities On The Superconductivity Of Bscco-2212, John Vastola

Honors Undergraduate Theses

BSCCO-2212 is a high-temperature cuprate superconductor whose microscopic behavior is currently poorly understood. In particular, it is unclear whether its order parameter is consistent with s-wave or d-wave symmetry. It has been suggested that its order parameter might take one of several forms that are consistent with d-wave behavior. We present some calculations using the many-body theory approach to superconductivity that suggest that such order parameters would lead to a suppression of the critical temperature in the presence of impurities. Because some experiments have suggested the critical temperature of BSCCO-2212 is relatively independent of the concentration of impurities, this lends …

Prospective Solid-State Photonic Cryocooler Based On The “Phonon-Deficit Effect”, Gurgen Melkonyan, Armen Gulian

Mathematics, Physics, and Computer Science Faculty Articles and Research

In this design microwave photons are propagating in a sapphire rod, and are being absorbed by a superconductor deposited on the surface of the rod. The frequency of the radiation is tuned to be less than the energy gap in the superconductor, so that the pair breaking is not taking place. This photon pumping redistributes the electron-hole quasiparticles: their distribution function is non-equilibrium, and the “phonon-deficit effect” takes place. There is a dielectric material deposited on top of superconductor, which serves asthe “cold finger” of the cooler. Its “acoustical density” is supposed to be smaller than that of the superconducting …

Reconstructions At The Interface In Complex Oxide Heterostructures With Strongly Correlated Electrons, Benjamin Gray

Graduate Theses and Dissertations

Strongly correlated oxides exhibit a rich spectrum of closely competing orders near the localized-itinerant Mott insulator transition leaving their ground states ripe with instabilities susceptible to small perturbations such as lattice distortions, variation in stoichiometry, magnetic and electric fields, etc. As the field of interfacial engineering has matured, these underlying instabilities in the electronic structure of correlated oxides continue to be leveraged to manipulate existing phases or search for emergent ones. The central theme is matching materials across the interface with disparate physical, chemical, electronic, or magnetic structure to harness interfacial reconstructions in the strongly coupled charge, spin, orbital, and …

Multiband S -Wave Topological Superconductors: Role Of Dimensionality And Magnetic Field Response, Shusa Deng, Gerardo Ortiz, Lorenza Viola

Dartmouth Scholarship

We further investigate a class of time-reversal-invariant two-band s-wave topological superconductors introduced earlier [Deng, Viola, and Ortiz, Phys. Rev. Lett. 108, 036803 (2012)]. Provided that a sign reversal between the two superconducting pairing gaps is realized, the topological phase diagram can be determined exactly (within mean field) in one and two dimensions as well as in three dimensions upon restricting to the excitation spectrum of time-reversal-invariant momentum modes. We show how, in the presence of time-reversal symmetry, Z2 invariants that distinguish between trivial and nontrivial quantum phases can be constructed by considering only one of the Kramers’ sectors …

Majorana Modes In Time-Reversal Invariant S -Wave Topological Superconductors, Shusa Deng, Lorenza Viola, Gerardo Ortiz

Dartmouth Scholarship

We present a time-reversal invariant s-wave superconductor supporting Majorana edge modes. The multiband character of the model together with spin-orbit coupling are key to realizing such a topological superconductor. We characterize the topological phase diagram by using a partial Chern number sum, and show that the latter is physically related to the parity of the fermion number of the time-reversal invariant modes. By taking the self-consistency constraint on the s-wave pairing gap into account, we also establish the possibility of a direct topological superconductor-to-topological insulator quantum phase transition.

Magnetic Properties Of Nb/Ni Superconducting / Ferromagnetic Multilayers, Sergiy A. Kryukov

Theses and Dissertations--Physics and Astronomy

Magnetic properties of Nb/Ni superconducting (SC) / ferromagnetic (FM) multilayers exhibit interesting properties near and below SC transition. A complex Field (H) – Temperature (T) phase boundary is observed in perpendicular and parallel orientation of ML with respect to DC field. We address the critical need to develop methods to make reliable magnetic measurements on SC thin films and ML, in spite of their extreme shape anisotropy and the strong diamagnetic response of the SC state.

Abrupt, highly reproducible “switching” of the SC state magnetization near the normal-state FM coercive fields has been observed in Nb/Ni ML. The SC penetration …

Quantum Analysis Of A Nonlinear Microwave Cavity-Embedded Dc Squid Displacement Detector, P. D. Nation, M. P. Blencowe, E. Buks

Dartmouth Scholarship

We carry out a quantum analysis of a dc superconducting quantum interference device (SQUID) mechanical displacement detector, comprising a SQUID with mechanically compliant loop segment, which is embedded in a microwave transmission line resonator. The SQUID is approximated as a nonlinear current-dependent inductance, inducing an external flux tunable nonlinear Duffing self-interaction term in the microwave resonator mode equation. Motion of the compliant SQUID loop segment is transduced inductively through changes in the external flux threading SQUID loop, giving a ponderomotive radiation pressure-type coupling between the microwave and mechanical resonator modes. Expressions are derived for the detector signal response and noise, …

Quantum Analysis Of A Linear Dc Squid Mechanical Displacement Detector, M. P. Blencowe, E. Buks

Dartmouth Scholarship

We provide a quantum analysis of a dc SQUID mechanical displacement detector within the subcritical Josephson current regime. A segment of the SQUID loop forms the mechanical resonator and motion of the latter is transduced inductively through changes in the flux threading the loop. Expressions are derived for the detector signal response and noise, which are used to evaluate the position and force detection sensitivity. We also investigate cooling of the mechanical resonator due to detector back reaction.

Decoherence And Recoherence In A Vibrating Rf Squid, Eyal Buks, M. P. Blencowe

Dartmouth Scholarship

We study an rf SQUID, in which a section of the loop is a freely suspended beam that is allowed to oscillate mechanically. The coupling between the rf SQUID and the mechanical resonator originates from the dependence of the total magnetic flux threading the loop on the displacement of the resonator. Motion of the latter affects the visibility of Rabi oscillations between the two lowest energy states of the rf SQUID. We address the feasibility of experimental observation of decoherence and recoherence, namely decay and rise of the visibility, in such a system.

Investigation Of The Superconducting Properties Of Niobium Radio-Frequency Cavities, Gianluigi Ciovati

Physics Theses & Dissertations

Radio-frequency (rf) superconducting cavities are widely used to increase the energy of a charged particle beam in particle accelerators. The maximum gradients of cavities made of bulk niobium have constantly improved over the last ten years and they are approaching the theoretical limit of the material. Nevertheless, rf tests of niobium cavities are still showing some "anomalous" losses (so-called "Q-drop"), characterized by a marked increase of the surface resistance at high rf fields, in absence of field emission. A low temperature "in-situ" baking under ultra-high vacuum has been successfully applied by several laboratories to reduce those losses and …

Thermal Propagation And Stability In Superconducting Films, Kenneth E. Gray, Robert T. Kampwirth, John F. Zasadzinski, Stephen P. Ducharme

Stephen Ducharme Publications

Thermal propagation and stable hot spots (normal domains) are studied in various high Tc superconducting films (Nb3Sn, Nb, NbN and Nb3Ge). The prediction of the thermal propagation velocity of the long-standing model of Broom and Rhoderick (1960) is verified quantitatively in the regime of its validity. A new energy balance model is shown to give reasonable quantitative agreement of the dependence of the propagation velocity on the length of short normal domains. The steady state (zero velocity) measurements indicate the existence of two distinct situations for films on high thermal conductivity (sapphire) substrates. For low power per unit area the …