Condensed Matter Physics Commons^™

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 …

Investigations Of Electrical And Physical Properties Of Ceramic Materials For Spacecraft Applications, Kevin Guerch, Jr Dennison

Presentations

No abstract provided.

Emergent Vortices At A Ferromagnetic Superconducting Oxide Interface, Alexander Paul Petrović, A. Paré, Tula R. Paudel, K. Lee, S. Holmes, Crispin H. W. Barnes, A. David, T. Wu, Evgeny Y. Tsymbal, C. Panagopoulos

Evgeny Tsymbal Publications

Understanding the cohabitation arrangements of ferromagnetism and superconductivity at the LaAlO₃/SrTiO₃ interface remains an open challenge. Probing this coexistence with sub-Kelvin magnetotransport experiments, we demonstrate that a hysteretic in-plane magnetoresistance develops below the superconducting transition for H < 0.15 T, independently of the carrier density or oxygen annealing. This hysteresis is argued to arise from vortex depinning within a thin (< 20 nm) superconducting layer, mediated by discrete ferromagnetic dipoles located solely above the layer. The pinning strength may be modified by varying the superconducting channel thickness via electric field-effect doping. No evidence is found for bulk magnetism or finite-momentum pairing, and we conclude that ferromagnetism is strictly confined to the interface, where it competes with superconductivity. Our work indicates that oxide interfaces are ideal candidate materials for the growth and analysis of nanoscale superconductor/ferromagnet hybrids.

Dual-Defect Model Of Electrostatic Discharge In Polymeric Dielectrics, Allen Andersen, Jr Dennison

Presentations

Electrostatic discharge (ESD) is a serious concern for spacecraft, high voltage power transmission, and other applications. A parallel plate capacitor geometry under high vacuum was used to apply increasing voltages across insulating samples until ESD breakdown and to apply sub-critical fields and observe time-to-breakdown. Transient arcing was frequently observed prior to complete ESD breakdown in both cases. Results are presented for two prototypical polymeric materials, low density polyethylene (LDPE) and polyimide (PI or Kapton HN™) in terms of both statistical and physics-based models.

Many electrical aging models are described by defect creation within the material from bond stress due to …

Small Satellite Space Environments Effects Test Facility, Jr Dennison, Kent Hartley, Lisa Montierth Phillipps, Justin Dekany, James S. Dyer, Robert Johnson

Presentations

No abstract provided.

Wigner High-Electron-Correlation Regime Of Nonuniform Density Systems: A Quantal-Density-Functional-Theory Study, Douglas Achan, Lou Massa, Viraht Sahni

Publications and Research

The Wigner regime of a system of electrons in an external field is characterized by a low electron density and a high electron-interaction energy relative to the kinetic energy. The low-correlation regime is in turn described by a high electron density and an electron-interaction energy smaller than the kinetic energy. The Wigner regime of a nonuniform-electron-density system is investigated via quantal density functional theory (QDFT). Within QDFT, the contributions of electron correlations due to the Pauli exclusion principle, Coulomb repulsion, and correlation-kinetic effects are separately delineated and explicitly defined. The nonuniform-electron-density system studied is that of the Hooke's atom in …

Small Satellite Space Environments Effects Test Facility, Jr Dennison, Kent Hartley, Lisa Montierth Phillipps, Justin Dekany, James S. Dyer, Robert H. Johnson

Conference Proceedings

A versatile test facility has been designed and built to study space environments effects on small satellites and system components. Testing for potentially environmental-induced modifications of small satellites is critical to avoid possible deleterious or catastrophic effects over the duration of space mission. This is increasingly more important as small satellite programs have longer mission lifetimes, expand to more harsh environments (such as polar or geosynchronous orbits), make more diverse and sensitive measurements, minimize shielding to reduce mass, and utilize more compact and sensitive electronics (often including untested off-the-shelf components). The vacuum chamber described here is particularly well suited for …

Environmental Testing Of Lasers For Jpl's Cold Atom Laboratory, Carey L. Baxter

STAR Program Research Presentations

NASA’s Cold Atom Lab (CAL) is a multi-user facility designed to study ultra-cold quantum gases in the microgravity environment of the International Space Station (ISS). One of the main goals of CAL is to explore the unknown territory of extremely low temperatures—possibly as low as the picokelvin range!—where new and fascinating quantum phenomena can be observed. At such temperatures matter stops behaving as particles and instead becomes macroscopic matter waves. CAL will be remotely controlled to perform a multitude of experiments and is scheduled to launch in 2016. In order to anticipate problems that might occur during and post-launch, including …

A Soft Condensed Matter Approach Towards Mathematical Modelling Of Mass Transport And Swelling In Food Grains, Michael Chapwanya, N. Misra

Articles

Soft condensed matter (SCM) physics has recently gained importance for a large class of engineering materials. The treatment of food materials from a soft matter perspective, however, is only at the surface and is gaining importance for understanding the complex phenomena and structure of foods. In this work, we present a theoretical treatment of navy beans from a SCM perspective to describe the hydration kinetics. We solve the transport equations within a porous matrix and employ the Flory–Huggin’s equation for polymer–solvent mixture to balance the osmotic pressure. The swelling of the legume seed is modelled as a moving boundary with …

Nanoscale Manipulation Of Pristine And Functionalized Freestanding Graphene Using Scanning Tunneling Microscopy, Matthew Ackerman

Graduate Theses and Dissertations

Over the past ten years the 2D material graphene has attracted an enourmous amount of attention from researchers from across diciplines and all over the world. Many of its outstanding electronic properties are present only when it is not interacting with a substrate but is instead freestanding. In this work I demonstrate that pristine and functionalized freestanding graphene can be imaged using a scanning tunneling microscope (STM) and that imaging a flexible 2D surface is fundamentally different from imaging a bulk material due to the attraction between the STM tip and the sample. This attraction can be used to manipulate …

Electron And Hole Drift Mobility Measurements On Thin Film Cdte Solar Cells, Qi Long, Steluta A. Dinca, Eric A. Schiff, Ming Yu, Jeremy Theil

Physics - All Scholarship

We report electron and hole drift mobilities in thin film polycrystalline CdTe solar cells based on photocarrier time-of-flight measurements. For a deposition process similar to that used for high-efficiency cells, the electron drift mobilities are in the range of 10–100 cm²/Vs, and holes are in the range of 1–10 cm²/Vs. The electron drift mobilities are about a thousand times smaller than those measured in single crystal CdTe with time-of-flight; the hole mobilities are about ten times smaller. Cells were examined before and after a vapor phase treatment with CdCl₂; treatment had little effect on …

Chemically Induced Jahn–Teller Ordering On Manganite Surfaces, Zheng Gai, Wenzhi Lin, John D. Burton, K. Fuchigami, Paul C. Snijders, T. Z. Ward, Evgeny Y. Tsymbal, J. Shen, Stephen Jesse, Sergei V. Kalinin, Arthur P. Baddorf

Evgeny Tsymbal Publications

Physical and electrochemical phenomena at the surfaces of transition metal oxides and their coupling to local functionality remains one of the enigmas of condensed matter physics. Understanding the emergent physical phenomena at surfaces requires the capability to probe the local composition, map order parameter fields and establish their coupling to electronic properties. Here we demonstrate that measuring the sub-30-pm displacements of atoms from high-symmetry positions in the atomically resolved scanning tunnelling microscopy allows the physical order parameter fields to be visualized in real space on the single-atom level. Here, this local crystallographic analysis is applied to the in-situ-grown manganite surfaces. …

Nonlinear Transport In Nanoscale Phase Separated Colossal Magnetoresistive Oxide Thin Films, V. R. Singh, L. Zhang, Anil Rajapitamahuni, N. Devries, Xia Hong

Materials Research Science and Engineering Center: Faculty Publications

We report a study of the I-V characteristics of 2.5–5.4 nm epitaxial La_1xSr_xMnO₃ (x = 0.33 and 0.5) and La_0.7Ca_0.3MnO₃ thin films. While La_0.67Sr_0.33MnO₃ films exhibit linear conduction over the entire temperature and magnetic field ranges investigated, we observe a strong correlation between the linearity of the I-V relation and the metal-insulator transition in highly phase separated La_0.5Sr_0.5MnO₃ and La_0.7Ca_0.3MnO₃ films. Linear I-V behavior has been observed in the high temperature paramagnetic insulating phase, and …

Below Gap Optical Absorption In Gaas Driven By Intense, Single-Cycle Coherent Transition Radiation, J. Goodfellow, Matthias Fuchs, D. Daranciang, S. Ghimire, F. Chen, H. Loos, D. A. Reis, A. S. Fisher, A. M. Lindenberg

Matthias Fuchs Publications

Single-cycle terahertz fields generated by coherent transition radiation from a relativistic electron beam are used to study the high field optical response of single crystal GaAs. Large amplitude changes in the sub-band-gap optical absorption are induced and probed dynamically by measuring the absorption of a broad-band optical beam generated by transition radiation from the same electron bunch, providing an absolutely synchronized pump and probe geometry. This modification of the optical properties is consistent with strong-field-induced electroabsorption. These processes are pertinent to a wide range of nonlinear terahertz-driven lightmatter interactions anticipated at accelerator-based sources.

Quantum Levitation Using Metamaterials, Venkatesh K. Pappakrishnan

Doctoral Dissertations

The emergence of an attractive vacuum force (Casimir force) between two purely dielectric materials can lead to an increase in the friction and the stiction effects in nanoscale devices, resulting in degradation or decreased performance. Thus, it is of high practical importance that the conditions for the reversal of the Casimir force from attractive to repulsive are identified. Although the repulsive Casimir force has been considered for high dielectric materials as an intermediate (between the plates) medium, so far no realistic system has been proposed that can demonstrate quantum levitation with air/vacuum as a host medium. Since air is the …