Condensed Matter Physics Commons^™

Characterizing Vibrationally Induced Damage Of Carbon Nanotube Forests, Jordan Lee, Brian Wood, Ashlan Keeler, Jr Dennison, T. -C. Shen

Presentations

No abstract provided.

Effects Of Radiation On The Electrostatic Discharge Of Polymers, Kip Quilter, Megan Loveland, Alexandra Hughlett, Jr Dennison

Posters

No abstract provided.

Real-Time Video Processing Of Arcing Events To Determine Coincidence, Jr Dennison, Gregory Wilson, Jonh Mojica Decena, Brian Wood

Posters

A system has been developed and tested for real-time monitoring of environmentally-induced electrostatic discharge events to test spacecraft component and material survivability. Simultaneous detection by several parallel methods in coincidence, enhances event detection, minimizes false signals, and collects complementary information to determine arc location, intensity, and timing. This research focuses on four computer-interfaced video cameras which provide spatial and temporal detection of visual arcing from the surface of various elements. A real time processing solution was developed which can calculate integrated intensities, sensitively detect intensity threshold events, and store relevant video frames from these threshold events. Post processing of this …

An Analysis Of Variations In Published Secondary Electron Yield Measurements Of Copper, Phil Lundgreen, Jr Dennison

Posters

No abstract provided.

Study Of The Kinetic Energy Densities Of Electrons As Applied To Quantum Dots In A Magnetic Field, Marlina Slamet, Viraht Sahni

Publications and Research

There are three expressions for the kinetic energy density t(r) expressed in terms of its quantal source, the single‐particle density matrix: t_A(r), the integrand of the kinetic energy expectation value; t_B(r), the trace of the kinetic energy tensor; t_C(r), a virial form in terms of the 'classical' kinetic field. These kinetic energy densities are studied by application to 'artificial atoms' or quantum dots in a magnetic field in a ground and excited singlet state. A comparison with the densities for natural atoms and molecules in their ground state is made. The near nucleus …

Using Coherent Phonons For Ultrafast Control Of The Dirac Node Of Srmnsb2, Christopher P. Weber, Madison G. Masten, Thomas C. Ogloza, Bryan S. Berggren, Michael K. L. Man, Keshav M. Dani, Jinyu Liu, Zhiqiang Mao, Dennis D. Klug, Adebayo A. Adeleke, Yansun Yao

Physics

SrMnSb₂ is a candidate Dirac semimetal whose electrons near the Y point have the linear dispersion and low mass of a Dirac cone. Here we demonstrate that ultrafast, 800-nm optical pulses can launch coherent phonon oscillations in Sr_0.94Mn_0.92Sb₂, particularly an A_g mode at 4.4 THz. Through first-principles calculations of the electronic and phononic structure of SrMnSb₂, we show that high-amplitude oscillations of this mode would displace the atoms in a way that transiently opens and closes a gap at the node of the Dirac cone. The ability to control the …

Excess Electron Screening Of Remote Donors And Mobility In Modern Gaas/Algaas Heterostructures, M. Sammon, Tianran Chen, B. I. Shklovskii

Physics & Engineering Faculty Publications

In modern GaAs/AlxGa1−xAs heterostructures with record high mobilities, a two-dimensional electron gas (2DEG) in a quantum well is provided by two remote donor δ-layers placed on both sides of the well. Each δ-layer is located within a narrow GaAs layer, flanked by narrow AlAs layers which capture excess electrons from donors but leave each of them localized in a compact dipole atom with a donor. Still excess electrons can hop between host donors to minimize their Coulomb energy. As a result they screen the random potential of donors dramatically. We numerically model the pseudoground state of excess electrons at a …

Tunable Two-Dimensional Dirac Nodal Nets, Ding-Fu Shao, Shu-Hui Zhang, Xiaoqian Dang, Evgeny Y. Tsymbal

Evgeny Tsymbal Publications

Nodal-line semimetals are characterized by symmetry-protected band crossing lines and are expected to exhibit nontrivial electronic properties. Connections of the multiple nodal lines, resulting in nodal nets, chains, or links, are envisioned to produce even more exotic quantum states. In this work, we propose a feasible approach to realize tunable nodal-line connections in real materials. We show that certain space group symmetries support the coexistence of the planar symmetry-enforced and accidental nodal lines, which are robust to spin-orbit coupling and can be tailored into intricate patterns by chemical substitution, pressure, or strain. Based on first-principles calculations, we identify nonsymmorphic centrosymmetric …

Magnetoelectric Memory Cells With Domain-Wall-Mediated Switching, Kirill Belashchenko, Oleg Tchernyshyov, Alexey Kovalev, Dmitri Nikonov

Kirill Belashchenko Publications

A magnetoelectric memory cell with domain - wall - mediated switching is implemented using a split gate architecture . The split gate architecture allows a domain wall to be trapped within a magnetoelectric antiferromagnetic ( MEAF ) active layer . An extension of this architecture applies to multiple gate linear arrays that can offer advantages in memory density , programmability , and logic functionality . Applying a small anisotropic in - plane shear strain to the MEAF can block domain wall precession to improve reliability and speed of switching

Characterization Of The Effects Of Radiation On Skeletal And Smooth Muscle Cells, Lori Caldwell, Charles Harding, Jr Dennison, Elizabeth Vargis

Posters

Muscular atrophy is a serious issue for extended spaceflight. Understanding and preventing the role of ionizing radiation in skeletal muscle loss would preserve the strength and endurance of astronauts and enable longer duration space travel and exploration. Irradiation was performed in the USU material physics group's Space Suvivability Test Chamber. C2C12 and CRL-1999 cells were exposed to dosages ranging from 0.5 - 36.8 Gy. Cell viability and growth rate were measured immediately following irradiation.

Long-Term Stability Of Ion-Beam Treated Space Polymers In Geo-Simulated Environment, J Kleiman, Z Iskanderova, L Krishtein, Jr Dennison, Brian Wood, C Best

Presentations

No abstract provided.

Long-Term Stability Of Ion-Beam Treated Space Polymers In Geo-Simulated Environment, J Kleiman, Z Iskanderova, C Best, Jr Dennison, Brian Wood

Presentations

It is a real challenge to reproduce various space environment conditions in ground-based facilities for testing of external space system materials and elements. This is due to the variety and complexity of the space environment conditions and their effects on materials and structures. The reliability of test results depends on accurate simulation of the critical factors and effects of the space environment for a particular mission. The main objectives of the simulation testing are to get the test results that are adequate to the material durability and functional behavior in a space environment.

As part of a large, multi-year program, …

Current-Driven Production Of Vortex-Antivortex Pairs In Planar Josephson Junction Arrays And Phase Cracks In Long-Range Order, Francisco Estellés-Duart, Miguel Ortuño, Andrés M. Somoza, Valerii M. Vinokur, Alex Gurevich

Physics Faculty Publications

Proliferation of topological defects like vortices and dislocations plays a key role in the physics of systems with long-range order, particularly, superconductivity and superfluidity in thin films, plasticity of solids, and melting of atomic monolayers. Topological defects are characterized by their topological charge reflecting fundamental symmetries and conservation laws of the system. Conservation of topological charge manifests itself in extreme stability of static topological defects because destruction of a single defect requires overcoming a huge energy barrier proportional to the system size. However, the stability of driven topological defects remains largely unexplored. Here we address this issue and investigate numerically …

Perpendicular Magnetic Anisotropy In Bulk And Thin-Film Cumnas For Antiferromagnetic Memory Applications, Ivan A. Zhuravlev, Anil Adhikari, K. D. Belashchenko

Kirill Belashchenko Publications

CuMnAs with perpendicular magnetic anisotropy is proposed as an active material for antiferromagnetic memory. Information can be stored in the antiferromagnetic domain state, while writing and readout can rely on the existence of surface magnetization. It is predicted, based on first-principles calculations, that easy-axis anisotropy can be achieved in bulk CuMnAs by substituting a few percent of As atoms by Ge, Si, Al, or B. This effect is attributed to the changing occupation of certain electronic bands near the Fermi level induced by hole doping. The calculated temperature dependence of the magnetic anisotropy does not exhibit any anomalies. Thin CuMnAs(001) …

Unconventional Anomalous Hall Effect From Antiferromagnetic Domain Walls Of Nd2Ir2O7 Thin Films, Woo Jin Kim, John H. Gruenewald, Taekoo Oh, Sangmo Cheon, Bongju Kim, Oleksandr B. Korneta, Hwanbeom Cho, Daesu Lee, Yoonkoo Kim, Miyoung Kim, Je-Geun Park, Bohm-Jung Yang, Ambrose Seo

Physics and Astronomy Faculty Publications

Ferroic domain walls (DWs) create different symmetries and ordered states compared with those in single-domain bulk materials. In particular, the DWs of an antiferromagnet with noncoplanar spin structure have a distinct symmetry that cannot be realized in those of their ferromagnet counterparts. In this paper, we show that an unconventional anomalous Hall effect (AHE) can arise from the DWs of a noncoplanar antiferromagnet, Nd₂Ir₂O₇. Bulk Nd₂Ir₂O₇ has a cubic symmetry; thus, its Hall signal should be zero without an applied magnetic field. The DWs generated in this material break …

Two-Dimensional Type-Ii Dirac Fermions In A Laalo3/Lanio3/Laalo3 Quantum Well, Lingling Tao, Evgeny Y. Tsymbal

Evgeny Tsymbal Publications

The type-II Dirac fermions that are characterized by a tilted Dirac cone and anisotropic magnetotransport properties have been recently proposed theoretically and confirmed experimentally. Here, we predict the emergence of two-dimensional (2D) type-II Dirac fermions in LaAlO₃/LaNiO₃/LaAlO₃ quantum-well structures. Using first-principles calculations and model analyses, we show that the Dirac points are formed at the crossing between the d_x²−y² and d_z² bands protected by the mirror symmetry. The energy position of the Dirac points can be tuned to appear at the Fermi energy by changing the quantum-well width. For …

Spatial And Temporal Correlations Of Xy Macro Spins, Robert Streubel, Noah Kent, Scott Dhuey, Andreas Scholl, Steve Kevan, Peter Fischer

Robert Streubel Papers

We use nano disk arrays with square and honeycomb symmetry to investigate magnetic phases and spin correlations of XY dipolar systems at the micro scale. Utilizing magnetization sensitive X-ray photoemission electron microscopy, we probe magnetic ground states and the “order-by-disorder” phenomenon predicted 30 years ago. We observe the antiferromagnetic striped ground state in square lattices, and 6-fold symmetric structures, including trigonal vortex lattices and disordered floating vortices, in the honeycomb lattice. The spin frustration in the honeycomb lattice causes a phase transition from a long-range ordered locked phase over a floating phase with quasi long-range order and indications of a …

Measuring The Practical Particle-In-A-Box: Orthorhombic Perovskite Nanocrystals, Brandon Mitchell, Eric Herrmann, Junhao Lin, Leyre Gomez, Chris De Weerd, Yasufumi Fujiwara, Kazutomo Suenaga, Tom Gregorkiewicz

Physics & Engineering Faculty Publications

A connection between condensed matter physics and basic quantum mechanics is demonstrated as we use the fundamental 3D particle-in-a-box model to explain the optical properties of semiconductor nanocrystals, which are substantially modified due to quantum confinement. We also discuss recent advances in the imaging and measurement capabilities of transmission electron microscopy, which have made it possible to directly image single nanocrystals while simultaneously measuring their characteristic absorption energies. We introduce the basic theory of nanocrystals and derive a simplified expression to approximate the optical bandgap energy of an orthorhombic nanocrystal. CsPbBr3 perovskite nanocrystals are used to demonstrate this model due …

Quantum And Classical Transport Of 2d Electrons In The Presence Of Long And Short Range Disorder, Jesse Kanter

Dissertations, Theses, and Capstone Projects

This work focuses on the study of electron transport of 2-D electron gas systems in relation to both fundamental properties of the systems such as disorder and scattering mechanisms, as well as unique magnetoresistance (MR) effects. A large portion of the discussion is built around the use of an in plane magnetic field to vary the ratio between the Zeeman energy between electrons of different spins and the Landau level spacing, creating a tool to control the quantization of the density of states (DOS).

This tool is first used to isolate Quantum Positive Magnetoresistance (QPMR), which grants insight to the …

Nmr Characterizations Of Candidate Battery Electrolytes, Stephen A. Munoz

Dissertations, Theses, and Capstone Projects

Enormous strides have been made in next-generation power sources to build a more sustainable society. Energy storage has become a limiting factor in our progress, and there are huge environmental and financial incentives to find the next step forward in battery technology. This work discusses NMR methods for characterizing materials for use in battery application, with a special focus on relaxometry and diffusometry. Examples are provided of various recent investigations involving novel candidate electrolyte materials with different collaborators. Works discussed in this thesis include: the characterization of a new disruptive solid polymer electrolyte technology, investigations of the dynamics of super …

Charge State Dynamics And Quantum Sensing With Defects In Diamond, Jacob D. Henshaw

Dissertations, Theses, and Capstone Projects

In recent years, defect centers in wide band gap semiconductors such as diamond, have received significant attention. Defects offer great utility as single photon emitters, nanoscale sensors, and quantum memories and registers for quantum computation. Critical to the utility of these defects, is their charge state.

In this dissertation, experiments surrounding the charge state dynamics and the carrier dynamics are performed and analyzed. Extensive studies of the ionization and recombination processes of defects in diamond, specifically, the Nitrogen Vacancy (NV) center, have been performed. Diffusion of ionized charge carriers has been imaged indirectly through the recapture of said carriers by …

Direct Experimental Evidence Of Toroidal Symmetry In A Lanthanide-Based Molecular Magnet, Qing Zhang

Dissertations, Theses, and Capstone Projects

Molecular magnets (MM) are finite clusters of identical exchange-coupled magnetic systems arranged within a crystalline array such that interactions between neighboring MMs are negligible. Their small size has proven them amenable test beds for the investigation of a wide range of fundamental quantum phenomena such as spin frustration quantum tunneling (QT) of magnetization and Neel vector quantum coherence and Berry phase interference.

Cases where MMs have been found to exhibit quantum wave-functions that evolve coherently are particularly interesting due to their potential for use in quantum information processing. Toroidal magnetic moments, a kind of MM, have fascinating properties that could …

Observation Of A Pressure-Induced Transition From Interlayer Ferromagnetism To Intralayer Antiferromagnetism In Sr4Ru3O10, H. Zheng, W. H. Song, J. Terzic, H. D. Zhao, Y. F. Ni, Lance E. Delong, P. Schlottmann, G. Cao

Physics and Astronomy Faculty Publications

Sr₄Ru₃O₁₀ is a Ruddlesden-Popper compound with triple Ru-O perovskite layers separated by Sr-O rock-salt layers. This compound presents a rare coexistence of interlayer (c-axis) ferromagnetism and intralayer (basal-plane) metamagnetism at ambient pressure. Here we report the observation of pressure-induced, intralayer itinerant antiferromagnetism arising from the interlayer ferromagnetism. The application of modest hydrostatic pressure generates an anisotropy that may cause a flattening and a tilting of RuO₆ octahedra. All magnetic and transport results from this study indicate these lattice distortions diminish the c-axis ferromagnetism and basal-plane metamagnetism, and induce a basal-plane antiferromagnetic state. …

Direct Observation Of Room-Temperature Out-Of-Plane Ferroelectricity And Tunneling Electroresistance At The Two-Dimensional Limit, H. Wang, Z. R. Liu, H. Y. Yoong, Tula R. Paudel, J. X. Xia, R. Guo, W. N. Lin, P. Yang, J. Wang, G. M. Chow, T. Venkatesan, Evgeny Y. Tsymbal, H. Tian, J. S. Chen

Evgeny Tsymbal Publications

Out-of-plane ferroelectricity with a high transition temperature in nanometer-scale films is required to miniaturize electronic devices. Direct visualization of stable ferroelectric polarization and its switching behavior in atomically thick films is critical for achieving this goal. Here, ferroelectric order at room temperature in the two-dimensional limit is demonstrated in tetragonal BiFeO₃ ultrathin films. Using aberration-corrected scanning transmission electron microscopy, we directly observed robust out-of-plane spontaneous polarization in one-unitcell-thick BiFeO₃ films. High-resolution piezoresponse force microscopy measurements show that the polarization is stable and switchable, whereas a tunneling electroresistance effect of up to 370% is achieved in BiFeO₃ films. …

Kinetic Effects In 2d And 3d Quantum Dots: Comparison Between High And Low Electron Correlation Regimes, Marlina Slamet, Viraht Sahni

Publications and Research

Kinetic related ground state properties of a two-electron 2D quantum dot in a magnetic field and a 3D quantum dot (Hooke's atom) are compared in the Wigner high (HEC) and low (LEC) electron correlation regimes. The HEC regime corresponds to low densities sufficient for the creation of a Wigner molecule. The LEC regime densities are similar to those of natural atoms and molecules. The results are determined employing exact closed-form analytical solutions of the Schrödinger-Pauli and Schrödinger equations, respectively. The properties studied are the local and nonlocal quantal sources of the density and the single particle density matrix; the kinetic …

Large T1 Contrast Enhancement Using Superparamagnetic Nanoparticles In Ultra-Low Field Mri, Xiaolu Yin, Stephen E. Russek, Gary Zabow, Fan Sun, Jeotikatan Mohapatra, Kathryn E. Keenan, Michael A. Boss, Hao Zeng, J. Ping Liu, Alexandrea Viert, Sy-Hwang Liou, John Moreland

Nebraska Center for Materials and Nanoscience: Faculty Publications

Superparamagnetic iron oxide nanoparticles (SPIONs) are widely investigated and utilized as magnetic resonance imaging (MRI) contrast and therapy agents due to their large magnetic moments. Local field inhomogeneities caused by these high magnetic moments are used to generate T₂ contrast in clinical high-field MRI, resulting in signal loss (darker contrast). Here we present strong T1 contrast enhancement (brighter contrast) from SPIONs (diameters from 11 nm to 22 nm) as observed in the ultra-low field (ULF) MRI at 0.13 mT. We have achieved a high longitudinal relaxivity for 18 nm SPION solutions, r1 = 615 s−1 mM−1, which is two …

Enhanced Acidity Of Acetic And Pyruvic Acids On The Surface Of Water, Alexis J. Eugene, Elizabeth A. Pillar, Agustín J. Colussi, Marcelo I. Guzman

Chemistry Faculty Publications

Understanding the acid–base behavior of carboxylic acids on aqueous interfaces is a fundamental issue in nature. Surface processes involving carboxylic acids such as acetic and pyruvic acids play roles in (1) the transport of nutrients through cell membranes, (2) the cycling of metabolites relevant to the origin of life, and (3) the photooxidative processing of biogenic and anthropogenic emissions in aerosols and atmospheric waters. Here, we report that 50% of gaseous acetic acid and pyruvic acid molecules transfer a proton to the surface of water at pH 2.8 and 1.8 units lower than their respective acidity constants pK_{a …}

Defect-Assisted Tunneling Electroresistance In Ferroelectric Tunnel Junctions, Konstantin Klyukin, Lingling Tao, Evgeny Y. Tsymbal, Vitaly Alexandrov

Evgeny Tsymbal Publications

Recent experimental results have demonstrated ferroelectricity in thin films of SrTiO₃ induced by antisite Ti_Sr defects. This opens a possibility to use SrTiO₃ as a barrier layer in ferroelectric tunnel junctions (FTJs)—emerging electronic devices promising for applications in nanoelectronics. Here using density functional theory combined with quantum-transport calculations applied to a prototypical Pt/SrTiO₃/Pt FTJ, we demonstrate that the localized in-gap energy states produced by the antisite Ti_Sr defects are responsible for the enhanced electron tunneling conductance which can be controlled by ferroelectric polarization. Our tight-binding modeling, which takes into account multiple defects, shows that …

Developing A Femtosecond Stimulated Raman Spectroscopy Experiment For Solid State Materials, Daniel Hammerland

Electronic Theses and Dissertations

Femtosecond Stimulated Raman Spectroscopy (FSRS) is a ultrafast spectroscopy technique first implemented by chemists to understand isomerization and other ultrafast molecular morphology changes by resolving vibrational dynamics[1, 2, 3]. FSRS has an unparalleled temporal and spectral resolution [4, 1, 5, 6] that arises as a result of a clever combination of picosecond and femtosecond pulses. However, despite this capability, FSRS has yet to be applied to modern materials in condensed matter physics. This thesis explores the design and implementation of FSRS to study two-dimensional materials in order to measure their quantum confined vibrational dynamics on utlrafast time scales.

Crystallographic Exploration Of Fundamental Technetium Species At Nonambient Conditions, Daniel S. Mast

UNLV Theses, Dissertations, Professional Papers, and Capstones

The study of mater under extreme conditions has yielded fascinating insight into the physical and chemical nature of materials that under more modest conditions are considered mundane but have quite unusual properties when under pressure. Examples of this are the lightest of elements found in the first two rows and in the heaviest elements of the lanthanide and actinide series. Pure elements, though the simplest possible chemical systems, have proven to be among the most complex and interesting. Technetium metal is a simple HCP transition metal that, due to its half-filled d-shell, has a rich chemistry and an important place …