Condensed Matter Physics Commons^™

Characterizing The Effects Of Radiation On Muscle Cells, Lori Caldwell, Charles Harding, Jr Dennison, Elizabeth Vargis

Posters

As longer space missions become more desirable to public and private institutions, the physiological impact on astronauts must be considered. One of the primary concerns for those spending time in low gravity and high radiation environments is muscle atrophy. A major cause of muscular atrophy is oxidative stress which is amplified by increased levels of ionizing radiation during spaceflight. Additionally, high levels of radiation can damage DNA, increasing the risk of cancer. Utah State University’s Space Environment Test Facility was used to irradiate C2C12 myoblasts and human vascular endothelial cells with a dosage mimicking that on the International Space Station …

Screening And Plasma Oscillations In An Electron Gas In The Hydrodynamic Approximation, Eugene B. Kolomeisky, Joseph P. Straley

Physics and Astronomy Faculty Publications

A hydrodynamic theory of screening in a generic electron gas of arbitrary dimensionality is given that encompasses all previously studied cases and clarifies the predictions of the many-body approach. We find that long-wavelength plasma oscillations are classical phenomena with quantum-mechanical effects playing no explicit role. The character of the oscillations is solely dictated by the dimensionality of the electron system and its equation of state in the neutral limit. Materials whose excitations are described by the Dirac dispersion law—such as doped graphene or a Weyl semimetal—are no exception to this rule.

Electron Yield Of Challenging Materials: Low Density Polyethylene And Carbon-Composite Nanodielectrics, Matthew Robertson, Jordan Lee, Jr Dennison

Presentations

The electron yield—the ratio of the number of emitted electrons to incident electrons—is a key material property that characterizes how materials will charge due to exposure to electron fluxes. The USU Materials Physics Group has developed expertise in measuring this for a wide array of conductors, semiconductors and insulators, including many challenging materials. The basic definitions associated with electron yield and how they are measured will be discussed. We will highlight many critical applications investigated at USU, particularly those associated with spacecraft charging as materials interact with space plasma environments. Electron irradiation experiments conducted to investigate the electron transport, charging, …

Electron Yield Of Challenging Materials: Low Density Polyethylene And Carbon-Composite Nanodielectrics, Matthew Robertson, Jordan Lee, Jr Dennison

Presentations

No abstract provided.

Highly Accelerated Test Method For Characterizing Likelihood Of Breakdown In Hvdc Dielectric Materials, Allen Andersen, Jr Dennison

Journal Articles

Increasing application and development of HVDC technologies emphasizes the need for improved characterization of candidate insulating materials. Accurately predicting the lifetime to breakdown of dielectric materials by means of accelerated voltage step-up to breakdown tests can be prohibitively time consuming. Step-up to breakdown tests with sufficiently slow voltage ramp rates that continuously monitor leakage current have detected a distribution of DC partial discharge (DCPD) events occurring prior to breakdown, which increase with increasing field. These DCPD distributions are shown to correlate strongly with the likelihood of breakdown for four common polymers. Given that hundreds of DCPD events are typically observed …

Detecting Majorana Fermion Induced Crossed Andreev Reflection, Lei Fang

Dissertations, Theses, and Capstone Projects

This dissertation is devoted to a study of detecting the Majorana fermion induced crossed Andreev reflection.

Majorana fermions are particles that constitute their own antiparticles. In condensed matter physics, Majorana fermions are zero energy modes that reside at edges or around vortices of topological superconductors. The special properties of Majorana fermions result in their potential to conduct topological quantum computation, which has been attracting a lot of current research. One of the most important issues in the field of the Majorana fermion physics now is to detect their existence in realistic systems. Among many classes of detecting methods, a transport …

Cubesat Space Environments Effects Studied In The Space Survivability Test Chamber, Alexander Souvall, Gregory Wilson, Ben Russon, Katie Gamaunt, Jr Dennison

Posters

No abstract provided.

Ambipolar Spin Diffusion In P-Type Gaas: A Case Where Spin Diffuses More Than Charge, F. Cadiz, V. Notot, J. Filipovic, Christopher P. Weber, L. Martinelli, A.C. H. Rowe, S. Arscott

Physics

We investigate the diffusion of charge and spin at 15 K in p-type GaAs, combining transient-grating and energy-resolved microluminescence measurements to cover a broad range of photoelectron density. At very low optical power, in a unipolar nondegenerate regime, charge and spin diffuse at the same rate, implying that the spin-drag effects are negligible. Upon increasing the photoelectron concentration up to about 1016 cm–3, the charge diffusion constant decreases because of ambipolar electrostatic interactions with the slower-diffusing holes while the spin diffusion constant is reduced only weakly by the ambipolar interaction. A further increase in the excitation power causes increases in …

Control Of Light-Matter Interaction In 2d Semiconductors, Zheng Sun

Dissertations, Theses, and Capstone Projects

In this thesis we discuss the control of light matter interaction in low dimensional nanostructure cavity light confining structures. These structures have controllable dispersion properties through design which can be exploited to modify the interaction of light and matter. We will discuss two different types of light confining microcavities: a dielectric cavity and a metal cavity. The specific design of the cavity gives rise to the confinement of the electric field in the center where the nano-materials are placed. In this work, the main material was on the new class of two- dimensional semiconductors of transition metal dichalcogenides (TMDs). Due …

Hopping Conductivity Of Electron Glass, Mingzhu Cui

Graduate Masters Theses

Hopping conductance between the sites in disordered systems is mapped to a random resistor network named Miller-Abrahams network. The conductance between two sites is in an exponential form depending on two parameters, the space separation and energy separation between sites. Our effort is focused on the visualization of the random resistor network. We find all the realizations for one electron hop and plot out the according random resistor networks. By comparing the random resistor network structures, we find that Coulomb interaction plays an important role in calculating the hopping conductance between sites. Furthermore, we rank the realizations by total energy …

Three-Dimensional Nanomagnetism, Amalio Fernández-Pacheco, Robert Streubel, Olivier Fruchart, Riccardo Hertel, Peter Fischer, Russell P. Cowburn

Robert Streubel Papers

Magnetic nanostructures are being developed for use in many aspects of our daily life, spanning areas such as data storage, sensing and biomedicine. Whereas patterned nanomagnets are traditionally two-dimensional planar structures, recent work is expanding nanomagnetism into three dimensions; a move triggered by the advance of unconventional synthesis methods and the discovery of new magnetic effects. In three-dimensional nanomagnets more complex magnetic configurations become possible, many with unprecedented properties. Here we review the creation of these structures and their implications for the emergence of new physics, the development of instrumentation and computational methods, and exploitation in numerous applications.

Machine Learning Phases Of Strongly Correlated Fermions, Kelvin Ch'ng, Juan Carrasquilla, Roger Melko, Ehsan Khatami

Faculty Publications

Machine learning offers an unprecedented perspective for the problem of classifying phases in condensed matter physics. We employ neural network machine learning techniques to distinguish finite-temperature phases of the strongly-correlated fermions on cubic lattices. We show that a three-dimensional convolutional network trained on auxiliary field configurations produced by quantum Monte Carlo simulations of the Hubbard model can correctly predict the magnetic phase diagram of the model at the average density of one (half filling). We then use the network, trained at half filling, to explore the trend in the transition temperature as the system is doped away from half filling. …

Evidence For A Low-Temperature Magnetic Ground State In Double-Perovskite Iridates With Ir5+(5D4) Ions, Jasminka Terzic, H. Zheng, Feng Ye, H. D. Zhao, P. Schlottmann, Lance E. De Long, S. J. Yuan, Gang Cao

Physics and Astronomy Faculty Publications

We report an unusual magnetic ground state in single-crystal, double-perovskite Ba₂YIrO₆ and Sr-doped Ba₂YIrO₆ with Ir⁵⁺(5d⁴) ions. Long-range magnetic order below 1.7 K is confirmed by dc magnetization, ac magnetic susceptibility, and heat-capacity measurements. The observed magnetic order is extraordinarily delicate and cannot be explained in terms of either a low-spin S = 1 state, or a singlet J_eff = 0 state imposed by the spin-orbit interactions (SOI). Alternatively, the magnetic ground state appears consistent with a SOI that competes with comparable Hund's rule coupling and inherently large …

Nanosecond X-Ray Photon Correlation Spectroscopy On Magnetic Skyrmions, M. H. Seaberg, B. Holladay, J. C.T. Lee, M. Sikorski, A. H. Reid, S. A. Montoya, G. L. Dakovski, J. D. Koralek, G. Coslovich, S. Moeller, W. F. Schlotter, R. Streubel, S. D. Kevan, P. Fischer, E. E. Fullerton, J. L. Turner, F. J. Decker, S. K. Sinha, S. Roy, J. J. Turner

Robert Streubel Papers

We report an x-ray photon correlation spectroscopy method that exploits the recent development of the two-pulse mode at the Linac Coherent Light Source. By using coherent resonant x-ray magnetic scattering, we studied spontaneous fluctuations on nanosecond time scales in thin films of multilayered Fe/Gd that exhibit ordered stripe and Skyrmion lattice phases. The correlation time of the fluctuations was found to differ between the Skyrmion phase and near the stripe-Skyrmion boundary. This technique will enable a significant new area of research on the study of equilibrium fluctuations in condensed matter.

Perspectives On The Distributions Of Esd Breakdowns For Spacecraft Charging Applications, Allen Andersen, Krysta Moser, Jr Dennison

Journal Articles

Electrostatic discharge (ESD) continues to pose significant risks to space missions despite decades of intense study. Tabulated values of material breakdown strength used in spacecraft charging models are often based on cursory measurements that may not be fully relevant to a given mission. Materials physics offers insight into the pertinent variables that affect breakdown and how to address them experimentally for spacecraft applications. We present measured distributions of ESD data across several test configurations for three polymeric materials that, taken together, begin to provide an understanding of how to estimate the likelihood of ESD events over a spacecraft’s mission lifetime. …

Pea System Modeling And Signal Processing For Measurement Of Volume Charge Distributions In Thin Dielectric Films, Lee H. Pearson, Jr Dennison, Erick W. Griffiths, Anthony C. Pearson

Journal Articles

This paper discusses our effort to develop advanced pulsed electroacoustic (PEA) measurement system capabilities that incorporate (1) improved signal processing tools for increased signal/noise ratios; and (2) integrated PEA modeling tools. In addition, we emphasize state-of-the-art system electronic components, integrated environmental controls, and sensor improvements required to achieve high spatial resolution while maintaining reasonable temporal resolution for both ambient and in vacuo measurements of thin dielectrics charged using electron beam injection, which is most applicable for spacecraft charging tests. PEA measurement systems provide an important tool to investigate the spatial extent and dynamic evolution of embedded charge distributions in thin …

Measuring And Modeling The Conductivity Of Highly Insulating Materials, David King

Senior Theses and Projects

Satellites and other spacecraft must be able to withstand hazardous conditions in order to be viable in their expected operating environments. One specific hazard that occurs due to incident radiation is spacecraft charging. Insulating materials, frequently used in spacecraft and other electrical equipment, while very good at preventing charge flow, also store charge very well. This can create problems; specifically, “if the charge decay time exceeds the orbital period, not all charge will be dissipated before orbital conditions act again to further charge the satellite. As the insulator accumulates charge, the electric field will rise until the insulator breaks down” …

Dependence Of Electrostatic Field Strength On Voltage Ramp Rate For Spacecraft Materials, Krysta Moser, Allen Andersen, Jr Dennison

Journal Articles

This work investigated the dependence of electrostatic field strength for spacecraft materials on voltage ramp rate, by applying an increasing incremental electrostatic field until electrostatic breakdown occurred. Tests on Kapton E found that at ramp rates two or three orders of magnitude lower than the maximum recommended rate, the electrostatic breakdown field, FESD was lower by a factor of two or more. This suggests that tabulated values of FESD, which have been used by the spacecraft charging community, could substantially overestimate FESD in common slowly evolving spacecraft situations. This study expanded these ramp rate tests to include a wider range …

Fabrication And Functionalization Of Carbon Nanocages For Use In Cfx Batteries., Nathan Smith

Electronic Theses and Dissertations

A relatively inexpensive method for obtaining high quality lithium-CF_x batteries is reported. Nickel acetate and citric acid are used to synthesize a precursor which is then annealed and subsequently etched to fabricate highly uniform 3 nm radius pristine CNCs. These CNCs are then functionalized with fluorine using an RF plasma system. The resulting fluorinated CNCs are then combined with a carbon binder and pressed onto a stainless steel mesh to form a CF_x cathode. This cathode is then tested in a coin cell primary battery with a lithium anode. Results indicate that a specific capacity of 660 mAh/g …

Novel Half-Metallic And Spin-Gapless Heusler Compounds, Yunlong Jin

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

This thesis is devoted to experimental studies of Heusler compounds CoFeCrAl, CoFeCrX (X = Si, Ge) and Mn₂PtSn. These Heusler alloys present an interesting class of ferromagnetic materials for spintronic applications since they are predicted to be spin gapless semiconductors and have half-metallic properties with 100 % spin polarization at the Fermi level. In this thesis, the structural, magnetic, spin-polarization and electron- transport properties of the fabricated alloys were studied. CoFeCrAl thin films deposited on MgO exhibit nearly perfect epitaxy and a high degree of L2₁ Heusler order. All considered types of chemical disorder destroy the spin-gapless …