Condensed Matter Physics Commons^™

Fate Of The Bose Insulator In The Limit Of Strong Localization And Low Cooper-Pair Density In Ultrathin Films, Shawna M. Hollen, G. E. Fernandes, J. M. Xu, J M. Valles Jr.

Physics & Astronomy

A Bose insulator composed of a low density of strongly localized Cooper pairs develops at the two-dimensional superconductor to insulator transition (SIT) in a number of thin film systems. Investigations of ultrathin amorphous PbBi films far from the SIT described here provide evidence that the Bose insulator gives way to a second insulating phase with decreasing film thickness. At a critical film thickness dc the magnetoresistance changes sign from positive, as expected for boson transport, to negative, as expected for fermion transport, signs of local Cooper-pair phase coherence effects on transport vanish, and the transport activation energy exhibits a kink. …

Pre-Breakdown Arcing And Electrostatic Discharge In Dielectrics Under High Dc Electric Field Stress, Allen Andersen, Jr Dennison

Journal Articles

Highly disordered insulating materials exposed to high electric fields will, over time, degrade and fail, potentially causing catastrophic damage to devices. Step-up to electrostatic discharge (ESD) tests were performed for two common polymer dielectrics, low density polyethylene and polyimide. Pre-breakdown transient current spikes or arcs were observed, using both slow and high speed detection. These pre-ESD discharge phenomena are explained in terms of breakdown modes and defect generation on a microscopic scale. The field at which pre-breakdown arcing begins was compared to the onset field for electrostatic discharge at which complete breakdown occurs for each material studied. We present evidence …

Pre-Breakdown Arcing And Electrostatic Discharge In Dielectrics Under High Dc Electric Field Stress, Allen Andersen, Jr Dennison

Conference Proceedings

Highly disordered insulating materials exposed to high electric fields will, over time, degrade and fail, potentially causing catastrophic damage to devices. Step-up electrostatic discharge (ESD) tests were performed for two common polymer dielectrics, low density polyethylene and polyimide. Prebreakdown transient current spikes or pre-arcs were observed, using both slow and high speed detection. These pre-ESD discharge phenomena are explained in terms of breakdown modes and defect generation on a microscopic scale. The field at which pre-breakdown arcing begins was compared to the onset field for electrostatic discharge at which complete breakdown begins to occur for each material. We present evidence …

Modeling The Energy Dependent Cathodoluminescent Intensity Of A Carbon Composite Material, Justin Christensen, Kelby T. Peterson, Justin Dekany, Jr Dennison

Presentations

When highly disordered insulating materials are subjected to energetic electron bombardment they can emit photons. This process is termed “cathodoluminescence.” This occurs in the space plasma environment and is an important phenomenon to understand when designing any object to be put into space. Light emitted from spacecraft materials can affect optical detection, and can cause stray-light contamination in space-based observatories. The Materials Physics Group at Utah State University uses an ultra-high vacuum chamber equipped with electron guns and a cryostat to control the sample temperature to simulate the space environment and to observe its affects on sample materials. Previous studies …

Discharge Breakdown Analyses, Sam Hansen, Jr Dennison, Allen Andersen

Presentations

Material breakdown due to Electrostatic discharge (ESD) is the primary cause of spacecraft damage due to environment interactions in space. This occurs when the space plasma fluxes charge a craft to high voltages where insulating craft materials then break down. This failure allows current to flow freely through the material, this can damage or destroy onboard electrical systems. My project focuses on the effects of these breakdowns on suspect materials commonly used for electrical insulation in space. The USU Material Physics Group has performed ESD tests on hundreds of samples to date. The ESD damage sites of these samples have …

Lifetimes Of Polymeric Dielectrics: A Dual-Defect Model, Allen Andersen, Jr Dennison

Presentations

Electrostatic discharge (ESD) can cause catastrophic failures in electronic devices. Estimating the lifetime of dielectrics under prolonged high field exposure is a major design concern for applications including spacecraft, high voltage DC power transmission, and semiconductor electronics. Dielectric strengths listed in engineering handbooks are primarily based on cursory measurements with poor repeatability and tend to overestimate ESD fields in real applications. Standard measurements subject test samples to ~500 V/s ramp rates until breakdown. We present the results of ESD studies in two prototypical polymer dielectrics using a ramp rate of ~20 V/4s until breakdown together with tests applying a static …

Cathodolumiescence Studies Of The Density Of States Of Disordered Silicon Dioxide, Jr Dennison, Amberly Evans Jensen

Presentations

Electron bombardment measurements have shown that disordered SiO2 exhibits cathodoluminescence, with an overall intensity that varies with incident electron beam energy and current density, sample temperature, exposure time, and wavelength. A simple model based on the defect density of states—used to explain electron transport in highly disordered insulating materials—has been extended to predict the relative cathodoluminescent intensity and spectral radiance for disordered SiO 2 as a function of these variables. The spectral radiance exhibited four distinct bands, corresponding to four distinct energy distributions of defect states within the band gap; each showed different temperature dependence. These localized defect or “trap” …

Space Effects Survivability Testing, Lisa Montierth Phillipps, Jr Dennison, Kent Hartley, Robert H. Johnson, Justin Dekany, James S. Dyer

Presentations

A versatile test facility has been designed to study the effects of space environment fluxes and radiation damage on small scale materials samples, system components, and small satellites. Cost-effective long-duration testing for potentially environmental-induced modifications is increasingly more important as small satellite programs have longer mission lifetimes, expand to more harsh environments, make more diverse and sensitive measurements, minimize shielding to reduce mass, and utilize more compact and sensitive electronics. The facility simulates environmental components including the neutral gas atmosphere, the solar spectrum, electron plasma fluxes, and temperature. The UV/VIS/NIR solar spectrum is simulated using a class AAA Solar Simulator …

Cathodoluminescence Events Coincident With Muon Detection, Kenneth Zia, Justin Dekany, Jr Dennison

Presentations

Samples of highly disordered insulating material have been irradiated with keV electron beams, resulting in three forms of electron induced light emission with differing duration: arcs (duration), “flares” (~100 s), and cathodoluminescence (as long as beam is on) [Dennison, 2013]. The arc and cathodoluminescence phenomena are well understood, while the flares’ origins are not. Flares were observed at intervals of ~2 per hr. This is within a factor of 2 for the expected muon cross section at an altitude of Logan, UT (1370 m) caused by high altitude cosmic rays; those high energy particles could have deposited sufficient energy throughout …

Cathodoluminescence Events Coincident With Muon Detection, Kenneth Zia

Senior Theses and Projects

No abstract provided.

Complex Band Structure Of Topologically Protected Edge States, Xiaoqian Dang, John D. Burton, Alan Kalitsov, Julian P. Velev, Evgeny Y. Tsymbal

Evgeny Tsymbal Publications

One of the great successes of modern condensed matter physics is the discovery of topological insulators (TIs). A thorough investigation of their properties could bring such materials from fundamental research to potential applications. Here, we report on theoretical investigations of the complex band structure (CBS) of two-dimensional (2D) TIs. We utilize the tight-binding form of the Bernevig, Hughes, and Zhang model as a prototype for a generic 2D TI. Based on this model, we outline the conditions that the CBS must satisfy in order to guarantee the presence of topologically protected edge states. Furthermore, we use the Green’s function technique …

Guesstimation: The Art Of Getting About The Right Answer, Jr Dennison

Presentations

No abstract provided.

A Dual-Defect Model For Predicting Lifetimes For Polymeric Discharges From Accelerated Testing, Allen Andersen, Jr Dennison

Posters

Electrostatic discharge (ESD) can cause catastrophic failures in electronic devices. Estimating the lifetime of dielectrics under prolonged high field exposure is a major design concern for applications including spacecraft, high voltage DC power transmission, and semiconductor electronics. Dielectric strengths listed in engineering handbooks are primarily based on cursory measurements with poor repeatability and tend to overestimate ESD fields in real applications. Standard measurements subject test samples to ≈500 V/s ramp rates until breakdown. We present the results of ESD studies in two prototypical polymer dielectrics using a ramp rate of ≈20 V/4s until breakdown, together with tests applying a …

Cathodolumiescence Studies Of The Density Of States Of Disordered Silicon Dioxide, Jr Dennison, Amberly Evans Jensen

Presentations

Electron bombardment measurements have shown that disordered SiO2 exhibits cathodoluminescence, with an overall intensity that varies with incident electron beam energy and current density, sample temperature, exposure time, and wavelength. A simple model based on the defect density of states—used to explain electron transport in highly disordered insulating materials—has been extended to predict the relative cathodoluminescent intensity and spectral radiance for disordered SiO2 as a function of these variables. The spectral radiance exhibited four distinct bands, corresponding to four distinct energy distributions of defect states within the band gap; each showed different temperature dependence. These localized defect or “trap” states …

Cathodoluminescence Events Coincident With Muon Detection, Kenneth Zia, Justin Dekany, Jr Dennison

Posters

Samples of highly disordered insulating material were irradiated with 1 keV electron beams, resulting in three forms of light emission with differing duration: arcs (<1 s duration), flares (~100 s), and cathodoluminescence (as long as beam is on). The arc and cathodoluminescence phenomena are well understood, while the flares are not. Flares were observed at intervals of ~2 per hr. This is within a factor of 2 for the expected muon crosssection at an altitude of Logan, UT (1370 m) caused by high altitude cosmic rays. Based on this suggestive evidence, we have proposed incorporation of standard muon coincidence detection apparatus into our vacuum cathode luminescence test facility. Measurements of the muon cross-section zenith angle and angle-dependence will provide calibration of the muon detector. If muon evidence coincides with the flare events, this will provide definitive evidence of the flare origin. We will discover whether a correlation between flares of charged sample are caused by transitory muons which trigger discharge and subsequent recharging during our testing of space materials.

Breakdown Analysis Of Electrostatic Discharge, Sam Hansen, Allen Andersen, Jr Dennison

Posters

Electrostatic discharge (ESD) and the associated material breakdown is the primary cause for spacecraft damage due to space environment interactions. This phenomenon occurs when the space plasma fluxes charge a craft to high voltages where insulating materials then break down. This failure allows current to flow freely through the material which; can damage or destroy onboard electrical systems. My work focuses on the effects of these breakdowns on suspect materials commonly used for electrical insulation in space. The USU Material Physics Group has performed ESD tests on hundreds of samples to date. The ESD damage sites of these samples have …

Structural Characterization Of Multimetallic Nanoparticles, Vineetha Mukundan

Open Access Dissertations

Bimetallic and trimetallic alloy nanoparticles have enhanced catalytic activities due to their unique structural properties. Using in situ time-resolved synchrotron based x-ray diffraction, we investigated the structural properties of nanoscale catalysts undergoing various heat treatments. Thermal treatment brings about changes in particle size, morphology, dispersion of metals on support, alloying, surface electronic properties, etc. First, the mechanisms of coalescence and grain growth in PtNiCo nanoparticles supported on planar silica on silicon were examined in detail in the temperature range 400-900°C. The sintering process in PtNiCo nanoparticles was found to be accompanied by lattice contraction and L1₀chemical ordering. …

Transport Studies Of Reentrant Integer Quantum Hall States Forming In The Two-Dimensional Electron Gas, Nianpei Deng

Open Access Dissertations

The two dimensional electron gas subjected to a magnetic field has been a model system in contemporary condensed matter physics which generated many beautiful experiments as well as novel fundamental concepts. These novel concepts are of broad interests and have benefited other fields of research. For example, the observations of conventional odd-denominator fractional quantum Hall states have enriched many-body physics with important concepts such as fractional statistics and composite fermions. The subsequent discovery of the enigmatic even-denominator ν=5/2 fractional quantum Hall state has led to more interesting concepts such as non-Abelian statistics and pairing of composite fermions which can be …

Spontaneous Time-Reversal Symmetry Breaking In Two Dimensional Electronic Systems, Wei Liu

Dissertations, Theses, and Capstone Projects

The discovery of high temperature superconductivity inspired a number of novel proposals, one of which, put forward by C.M.Varma, involves the breaking of time-reversal symmetry to explain the physics of the underdoped pseudogap phase. It was proposed that time-reversal symmetry is spontaneously broken as a result of strong repulsion between the Cu-O electrons to form loop-currents in the system.

In this work, we developed a general theory to study the quantum phase transitions in the 2 dimensional strongly interacting electronic systems in which time-reversal symmetry is spontaneously broken in the ground state. We first applied the theory of magnetic groups …

Transport And Optical Properties Of Low-Dimensional Complex Systems, Andrii Iurov

Dissertations, Theses, and Capstone Projects

Over the last five years of my research work, I, my research was mainly concerned with certain crucial tunneling, transport and optical properties of novel low-dimensional graphitic and carbon-based materials as well as topological insulators. Both single-electron and many-body problems were addressed. We investigated the Dirac electrons transmission through a potential barrier in the presence of circularly polarized light. An anomalous photon-assisted enhanced transmission is predicted and explained in a comparison with the well-known Klein paradox. It is demonstrated that the perfect transmission for nearly-head-on collision in an infinite graphene is suppressed in gapped dressed states of electrons, which is …