Condensed Matter Physics Commons^™

Developing A Safe Test System For High-Energy Electron Flux Environments Testing, Heather Tippets

Posters

In order to predict and mitigate adverse environmental effects prone to spacecraft in orbit about earth, a versatile pre-launch test capability for assessment and verification of small satellites, systems, and components was developed by Utah State University’s Materials Physics Group. To further diversify this project, a 100 mCi strontium-90 beta radiation source (0.5 MeV – 2.5 MeV) was exploited to simulate high energy electron flux characteristic of geostationary orbit. Various samples including in-the-loop hardware, spacecraft materials, optical components, and solar arrays will be irradiated to gain a better understanding how these materials and electronics break down in space environments. For …

Dispersion Of Electric-Field-Induced Faraday Effect In Magnetoelectric Cr2o3, J. Wang, Christian Binek

Christian Binek Publications

The frequency dependence of the electric-field-induced magneto-optical Faraday effect is investigated in the magnetoelectric antiferromagnet chromia. Two electrically induced Faraday signals superimpose in proportion to the linear magnetoelectric susceptibility α and the antiferromagnetic order parameter η. The relative strength of these contributions is determined by the frequency of the probing light and can be tuned between extreme characteristics following the temperature dependence of α or η. The frequency dependence is analyzed in terms of electric dipole transitions of perturbed Cr³⁺ crystal-field states. The results allow us to measure voltage-controlled selection, isothermal switching, and temperature dependence of η in …

Characteristic Length Scales Of The Secondary Relaxations In Glass-Forming Glycerol, Sudipta Gupta, Eugene Mamontov, Niina Jalarvo, Laura Stingaciu, Michael Ohl

Faculty Publications

We investigate the secondary relaxations and their link to the main structural relaxation in glass-forming liquids using glycerol as a model system. We analyze the incoherent neutron scattering signal dependence on the scattering momentum transfer, Q , in order to obtain the characteristic length scale for different secondary relaxations. Such a capability of neutron scattering makes it somewhat unique and highly complementary to the traditional techniques of glass physics, such as light scattering and broadband dielectric spectroscopy, which provide information on the time scale, but not the length scales, of relaxation processes. The choice of suitable neutron scattering techniques depends …

A Novel Methodology For Spatial Damage Detection And Imaging Using A Distributed Carbon Nanotube-Based Composite Sensor Combined With Electrical Impedance Tomography, Hongbo Dai, Gerard J. Gallo, Thomas Schumacher, Erik T. Thostenson

Civil and Environmental Engineering Faculty Publications and Presentations

This paper describes a novel non-destructive evaluation methodology for imaging of damage in composite materials using the electrical impedance tomography (EIT) technique applied to a distributed carbon nanotube-based sensor. The sensor consists of a nonwoven aramid fabric, which was first coated with nanotubes using a solution casting approach and then infused with epoxy resin through the vacuum assisted resin transfer molding technique. Finally, this composite sensor is cured to become a mechanically-robust, electromechanically-sensitive, and highly customizable distributed two-dimensional sensor which can be adhered to virtually any substrate. By assuming that damage on the sensor directly affects its conductivity, a difference …

Emergence Of Helical Edge Conduction In Graphene At The Ν = 0 Quantum Hall State, Pavel Tikhonov, Efrat Shimshoni, H. A. Fertig, Ganpathy Murthy

Physics and Astronomy Faculty Publications

The conductance of graphene subject to a strong, tilted magnetic field exhibits a dramatic change from insulating to conducting behavior with tilt angle, regarded as evidence for the transition from a canted antiferromagnetic (CAF) to a ferromagnetic (FM) ν = 0 quantum Hall state. We develop a theory for the electric transport in this system based on the spin-charge connection, whereby the evolution in the nature of collective spin excitations is reflected in the charge-carrying modes. To this end, we derive an effective field-theoretical description of the low-energy excitations, associated with quantum fluctuations of the spin-valley domain-wall ground-state configuration which …

Exciton Dynamics And Many Body Interactions In Layered Semiconducting Materials Revealed With Non-Linear Coherent Spectroscopy, Prasenjit Dey

USF Tampa Graduate Theses and Dissertations

Atomically thin, semiconducting transition metal dichalogenides (TMDs), a special class of layered semiconductors, that can be shaped as a perfect two dimensional material, have garnered a lot of attention owing to their fascinating electronic properties which are achievable at the extreme nanoscale. In contrast to graphene, the most celebrated two-dimensional (2D) material thus far; TMDs exhibit a direct band gap in the monolayer regime. The presence of a non-zero bandgap along with the broken inversion symmetry in the monolayer limit brands semiconducting TMDs as the perfect candidate for future optoelectronic and valleytronics-based device application. These remarkable discoveries demand exploration of …

Developing A Safe Test System For High-Energy Electron Flux Environments Testing, Heather Tippets

Senior Theses and Projects

In order to predict and mitigate adverse environmental effects on spacecraft in orbit about Earth, a versatile pre-launch test capability for assessment and verification of small satellites, systems, and components was developed by Utah State University’s Materials Physics Group. To further diversify this project, a 100 mCi Sr-90 beta radiation source (0.5 MeV – 2.5 MeV) is exploited to simulate the high energy electron flux of geostationary orbit. Various samples including in-the-loop hardware, spacecraft materials, optical components, and solar arrays are irradiated to gain a better understanding of how these materials and electronics break down in space environments. For employee …

Radiation Safety Design For High Energy Electron Flux Environments Testing, Heather Tippets

Senior Theses and Projects

No abstract provided.

New Type Of Al-Based Decagonal Quasicrystal In Al60Cr20Fe10Si10 Alloy, Zhanbing He, Haikun Ma, Hua Li, Xingzhong Li, Xiuliang Ma

Nebraska Center for Materials and Nanoscience: Faculty Publications

A new kind of decagonal quasicrystal (DQC) with a periodicity of 1.23 nm was observed in the as-cast quaternary Al₆₀Cr₂₀Fe₁₀Si₁₀ alloy. The intensity distribution of some spots in the selected-area electron diffraction pattern along the tenfold zone axis was found to be different from other Al-based DQCs. High-angle annular dark-field scanning transmission electron microscopy was adopted to reveal the structural features at an atomic level. Both the tenfold symmetry and symmetry-broken decagonal (D) clusters of 1.91 nm in diameter were found, but with structural characteristics different from the corresponding D clusters in the …

Engineering Interfacial Energy Profile By Changing The Substrate Terminating Plane In Perovskite Heterointerfaces, S. Roy, Alim Solmaz, John D. Burton, Mark Huijben, Guus Rijnders, Evgeny Y. Tsymbal, T. Banerjee

Evgeny Tsymbal Publications

Atomically engineered oxide heterointerfaces show a range of novel phenomena not present in their bulk form, thus providing an additional knob to tune the functional properties across such interfaces. Here we show that for an oxide Schottky interface between metallic SrRuO₃ and semiconducting Nb doped SrTiO₃ (Nb:STO) the terminating surface of the substrate plays a crucial role in determining the electronic transport across it. Interestingly this is achieved by engineering a monolayer of a charge-neutral SrO layer across the Schottky interface and not by the insertion of charged layers at the interface, as has been demonstrated earlier. These …

Stability Of Skyrmion Lattices And Symmetries Of Quasi-Two-Dimensional Chiral Magnets, Utkan Güngördü, Rabindra Nepal, Oleg A. Tretiakov, Kirill D. Belashchenko, Alexey Kovalev

Materials Research Science and Engineering Center: Faculty Publications

Recently there has been substantial interest in realizations of skyrmions, in particular in quasi-two-dimensional (2D) systems due to increased stability resulting from reduced dimensionality. A stable skyrmion, representing the smallest realizable magnetic texture, could be an ideal element for ultradense magnetic memories. Here we use the most general form of the quasi-2D free energy with Dzyaloshinskii-Moriya interactions constructed from general symmetry considerations reflecting the underlying system. We predict that the skyrmion phase is robust and it is present even when the system lacks the in-plane rotational symmetry. In fact, the lowered symmetry leads to increased stability of vortex-antivortex lattices with …

Degradation Effects Of Ionizing Radiation On Commercially Available Spacecraft Components, Alex Souvall

Senior Theses and Projects

No abstract provided.

First-Order Superfluid To Valence-Bond Solid Phase Transitions In Easy-Plane Su(N) Magnets For Small N, Jonathan D'Emidio, Ribhu K. Kaul

Physics and Astronomy Faculty Publications

We consider the easy-plane limit of bipartite SU(N) Heisenberg Hamiltonians, which have a fundamental representation on one sublattice and the conjugate to fundamental on the other sublattice. For N = 2 the easy plane limit of the SU(2) Heisenberg model is the well-known quantum XY model of a lattice superfluid. We introduce a logical method to generalize the quantum XY model to arbitrary N, which keeps the Hamiltonian sign-free. We show that these quantum Hamiltonians have a world-line representation as the statistical mechanics of certain tightly packed loop models of N colors in which neighboring loops are …

Ν = 1/2 Landau Level: Half-Empty Versus Half-Full, Ganpathy Murthy, R. Shankar

Physics and Astronomy Faculty Publications

We show here that an extension of the Hamiltonian theory developed by us over the years furnishes a composite fermion (CF) description of the ν = 1/2 state that is particle-hole (PH) symmetric, has a charge density that obeys the magnetic translation algebra of the lowest Landau level (LLL), and exhibits cherished ideas from highly successful wave functions, such as a neutral quasiparticle with a certain dipole moment related to its momentum. We also a provide an extension away from ν = 1/2, which has the features from ν = 1/2 and implements the PH transformation on the LLL as …

Ultrafast Spectroscopy And Energy Transfer In An Organic/Inorganic Composite Of Zinc Oxide And Graphite Oxide, Jeff A. Secor

Dissertations, Theses, and Capstone Projects

The energy transfers and nature of defect levels of an organic/inorganic composite of Zinc Oxide and Graphite are studied with multidimensional spectroscopy. The edge and surface states of each composite are uncovered using excitation emission experiments showing which defect states are mediating the energy transfer from the metal oxide to the graphite oxide. Multidimensional time resolved spectroscopy further describes the effect of the carbon phase on the energy transfer pathways in the material.

Properties Of Type-Ii Znte/Znse Submonolayer Quantum Dots Studied Via Excitonic Aharonov-Bohm Effect And Polarized Optical Spectroscopy, Haojie Ji

Dissertations, Theses, and Capstone Projects

In this thesis I develop understanding of the fundamental physical and material properties of type-II ZnTe/ZnSe submonolayer quantum dots (QDs), grown via combination of molecular beam epitaxy (MBE) and migration enhanced epitaxy (MEE). I use magneto-photoluminescence, including excitonic Aharonov-Bohm (AB) effect and polarized optical spectroscopy as the primary tools in this work.

I present previous studies as well as the background of optical and magneto-optical processes in semiconductor nanostructures and introduce the experimental methods in Chapters 1 - 3.

In Chapter 4 I focus on the excitonic AB effect in the type-II QDs. I develop a lateral tightly-bound exciton model …

Canonical Models Of Dielectric Response, D. Mark Riffe

All Physics Faculty Publications

The interaction of electromagnetic fields with a solid is characterized by several interconnected response functions: the dielectric function ε(ω), index of refraction N(ω), conductivity σ(ω), and optical impedance Z(ω). Here we utilize three canonical models of dielectric response -- the damped harmonic oscillator, Debye polarization response, and the Drude model -- to discuss these four optical response functions. Special emphasis is devoted to the response of a Drude metal. Our main focus is on electromagnetic wave propagation through a material. We also discuss the relaxation of charge fluctuations within the context of the three canonical models of response.

Modification Of The G-Phonon Mode Of Graphene By Nitrogen Doping, Pavel V. Lukashev, Liuyan Zhao, Tula R. Paudel, Theanne Schiros, Noah Hurley, Evgeny Y. Tsymbal, Aron Pinczuk, Abhay Pasupathy, Rui He

Evgeny Tsymbal Publications

The effect of nitrogen doping on the phonon spectra of graphene is analyzed. In particular, we employ first-principles calculations and scanning Raman analysis to investigate the dependence of phonon frequencies in graphene on the concentration of nitrogen dopants. We demonstrate that the G phonon frequency shows oscillatory behavior as a function of nitrogen concentration. We analyze different mechanisms which could potentially be responsible for this behavior, such as Friedel charge oscillations around the localized nitrogen impurity atom, the bond length change between nitrogen impurity and its nearest neighbor carbon atoms, and the long-range interactions of the nitrogen point defects. We …

Vortex Circulation And Polarity Patterns In Closely Packed Cap Arrays, Robert Streubel, Florian Kronast, Christopher F. Reiche, Thomas Mühl, Anja U.B. Wolter, Oliver G. Schmidt, Denys Makarov

Robert Streubel Papers

We studied curvature-driven modifications to the magnetostatic coupling of vortex circulation and polarity in soft-magnetic closely packed cap arrays. A phase diagram for the magnetic remanent/transition states at room temperature as a function of diameter and thickness was assembled. For specimens with vortex remanent state (40 nm-thick Permalloy on 330 nm spherical nanoparticles), both vortex circulation and polarity were visualized. Intercap coupling upon vortex nucleation leads to the formation of vortex circulation patterns in closely packed arrays. The remanent circulation pattern can be tailored choosing the direction of the applied magnetic field with respect to the symmetry axis of the …

Tunneling Anisotropic Magnetoresistance In A Magnetic Tunnel Junction With Half-Metallic Electrodes, John D. Burton, Evgeny Y. Tsymbal

Evgeny Tsymbal Publications

Tunneling anisotropic magnetoresistance (TAMR) is the difference in resistance of a magnetic tunnel junction due to a change in magnetization direction of one or both magnetic electrodes with respect to the flow of current. We present the results of first-principles density functional calculations of the TAMR effect in magnetic tunnel junctions with La_0.7Sr_0.3MnO₃ (LSMO) electrodes and a SrTiO₃ (STO) tunneling barrier. We find an ∼500% difference in resistance between magnetization in the plane and out of the plane. This large TAMR effect originates from the half-metallic nature of LSMO: When magnetization is out of …

Collective Bulk And Edge Modes Through The Quantum Phase Transition In Graphene At Ν = 0, Ganpathy Murthy, Efrat Shimshoni, H. A. Fertig

Physics and Astronomy Faculty Publications

Undoped graphene in a strong, tilted magnetic field exhibits a radical change in conduction upon changing the tilt angle, which can be attributed to a quantum phase transition from a canted antiferromagnetic (CAF) to a ferromagnetic (FM) bulk state at filling factor ν = 0. This behavior signifies a change in the nature of the collective ground state and excitations across the transition. Using the time-dependent Hartree-Fock approximation, we study the collective neutral (particle-hole) excitations in the two phases, both in the bulk and on the edge of the system. The CAF has gapless neutral modes in the bulk, whereas …

Predictive Formula For Electron Range Over A Large Span Of Energy, Anne C. Starley

Senior Theses and Projects

No abstract provided.

Finite-Size Scaling Of Flexoelectricity In Langmuir-Blodgett Polymer Thin Films, Shashi Poddar, Keith Foreman, Shireen Adenwalla, Stephen Ducharme

Stephen Ducharme Publications

The flexoelectric effect, which is a linear coupling between a strain gradient and electrical polarization, is a fundamental electromechanical property of all materials with potential for use in nanoscale devices, where strain gradients can be quite large. We report a study of the dependence of the flexoelectric response on thickness in ultrathin films of polar and non-polar polymers. The measurements of the flexoelectric response in non-polar polyethylene and the polar relaxor polymer polyvinylidene-co-trifluoroethylene-co-chlorofluoroethylene were made using a bent cantilever method and corrected for the contribution from the electrode oxide. The results show that the value of …

Electron Diffraction Study Of Cobalt-Rich Hf-Co, Xingzhong Li, Yunlong Jin, Jeffrey E. Shield, Ralph Skomski, David J. Sellmyer

Nebraska Center for Materials and Nanoscience: Faculty Publications

Intermetallic compounds having compositions from HfCo₄ to HfCo₈ were investigated by transmission electron microscopy, selected-area electron diffraction, and energy-dispersive x-ray spectroscopy. A major crystalline phase, closely related to the orthorhombic Zr₂Co₁₁ phase in structure, has been observed in the samples with the composition ranges from HfCo₆ to HfCo₈. The phase, referred to as either Hf₂Co₁₁ or HfCo₇ phase in the literature, is actually one common phase, having a broad composition range and referred to as μ-phase in the present paper. In addition to the μ-phase, we …

The Space Survivability Test Chamber, Alex Souvall, Benjamin Russon, Brian Wood, Gregory Wilson, Jr Dennison

Posters

No abstract provided.

The First Calibration Of Sbf Using Multi-Conjugate Adaptive Optics, Zachary Gibson, Joseph B. Jenson, John P. Blakeslee, Mischa Schirmer

Presentations

We measured Surface Brightness FluctuaIons (SBF) in three galaxies, ESO137-G006, NGC 3309, and NGC 5128, using the GeMS MulI-Conjugate AdapIve OpIcs (MCAO) system on the Gemini South telescope. ESO137-G006 is located in the Norma Cluster, NGC 3309 is located in the Hydra Cluster, while NGC 5128, also known as Centaurus A, is a nearby galaxy with numerous other distance measurements, including Cepheids. These galaxies were observed as a path finder to establish the SBF technique using the MCAO system. The J and Ks-band images taken with MCAO were astrometrically corrected and combined using the THELI so_ware.1 This method allowed us …

Predictive Formula For Electron Penetration Depth Of Diverse Materials Over Large Energy Ranges, Anne C. Starley, Gregory Wilson, Lisa D. Montierth, Jr Dennison

Conference Proceedings

An empirical model that predicts the approximate electron penetration depth—or range—of some common materials has been extended to predict the range for a broad assortment of other materials. The electron range of a material is the maximum distance electrons can travel through a material, before losing all of their incident kinetic energy. The original model used the Continuous Slow Down Approximation (CSDA) for energy deposition in a material to develop a composite analytical formula which estimated the range from10 MeV with an uncertainty of200 materials which have tabulated range and inelastic mean free path data in the NIST ESTAR and …

Voltage Ramp-Rate Dependence Of Dc Breakdown In Polymeric Insulators: Physical Models Versus Data, Allen Andersen, Krysta Moser, Jr Dennison

Conference Proceedings

The standard handbook values for dielectric breakdown strength of necessity come from accelerated test methods. In some cases, the breakdown voltage may vary significantly with voltage ramp rates; therefore, a theoretical model for the ramp-rate dependence of breakdown is needed to extrapolate from realistic tests to long-duration material service lifetimes. Series of step-up to breakdown tests were performed for ramp rates from 0.5 to 500 V/s for biaxially-oriented polypropylene (BOPP), low density polyethylene (LDPE), and polyimide (PI) films. The data were fit with standard empirical methods, as well as two physics-based defect-driven models. Empirical models can be fit to a …

Space Environment Effects Of Ionizing Radiation On Seed Germination And Growth, Alexander Souvall, Jr Dennison, Takayuki Sakai, Yuta Takahashi, Midori Morikawa, Shusuke Okita, Akihiro Nagata, Toshihiro Kameda, Shaunda Wenger

Presentations

No abstract provided.

Thermal Effects On Spin Currents In Non-Local Metallic Spin Valves, Alex Hojem

Electronic Theses and Dissertations

The study of non-local spin valves (NLSVs) has recently proven to be a fertile area for both applied and fundamental research in nanomagnetism due to the unique ability to separate charge currents and spin currents. NLSVs may also prove essential for a new class of high-density hard disk read heads due to their favorable scalability. Recent studies have shown thermal effects created by high current densities play a significant role in the response of NLSVs. These thermal effects also provide the opportunity to create a pure spin current from thermal gradients via a mechanism call the spin dependent Seebeck effect …