Condensed Matter Physics Commons^™

Discrimination Between Spin-Dependent Charge Transport And Spin-Dependent Recombination In Π-Conjugated Polymers By Correlated Current And Electroluminescence-Detected Magnetic Resonance, Marzieh Kavand, Douglas Baird, Kipp Van Schooten, Hans Malissa

Dartmouth Scholarship

Spin-dependent processes play a crucial role in organic electronic devices. Spin coherence can give rise to spin mixing due to a number of processes such as hyperfine coupling, and leads to a range of magnetic field effects. However, it is not straightforward to differentiate between pure single-carrier spin-dependent transport processes which control the current and therefore the electroluminescence, and spin-dependent electron-hole recombination which determines the electroluminescence yield and in turn modulates the current. We therefore investigate the correlation between the dynamics of spin-dependent electric current and spin-dependent electroluminescence in two derivatives of the conjugated polymer poly(phenylene-vinylene) using simultaneously measured pulsed …

Interaction-Induced Dirac Fermions From Quadratic Band Touching In Bilayer Graphene, Sumiran Pujari, Thomas C. Lang, Ganpathy Murthy, Ribhu K. Kaul

Physics and Astronomy Faculty Publications

We revisit the effect of local interactions on the quadratic band touching (QBT) of the Bernal honeycomb bilayer model using renormalization group (RG) arguments and quantum Monte Carlo (QMC) simulations. We present a RG argument which predicts, contrary to previous studies, that weak interactions do not flow to strong coupling even if the free dispersion has a QBT. Instead, they generate a linear term in the dispersion, which causes the interactions to flow back to weak coupling. Consistent with this RG scenario, in unbiased QMC simulations of the Hubbard model we find compelling evidence that antiferromagnetism turns on at a …

Magnetism In Curved Geometries, Robert Streubel, Peter Fischer, Florian Kronast, Volodymyr P. Kravchuk, Denis D. Sheka, Yuri Gaididei, Oliver G. Schmidt, Denys Makarov

Robert Streubel Papers

Extending planar two-dimensional structures into the three-dimensional space has become a general trend in multiple disciplines, including electronics, photonics, plasmonics and magnetics. This approach provides means to modify conventional or to launch novel functionalities by tailoring the geometry of an object, e.g. its local curvature. In a generic electronic system, curvature results in the appearance of scalar and vector geometric potentials inducing anisotropic and chiral effects. In the specific case of magnetism, even in the simplest case of a curved anisotropic Heisenberg magnet, the curvilinear geometry manifests two exchange-driven interactions, namely effective anisotropy and antisymmetric exchange, i.e. Dzyaloshinskii-Moriya-like interaction. As …

Electron Correlations In Local Effective Potential Theory, Viraht Sahni, Xiao-Yin Pan, Tao Yang

Publications and Research

Local effective potential theory, both stationary-state and time-dependent, constitutes the mapping from a system of electrons in an external field to one of the noninteracting fermions possessing the same basic variable such as the density, thereby enabling the determination of the energy and other properties of the electronic system. This paper is a description via Quantal Density Functional Theory (QDFT) of the electron correlations that must be accounted for in such a mapping. It is proved through QDFT that independent of the form of external field, (a) it is possible to map to a model system possessing all the basic …

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

Posters

CubeSats are particularly susceptible to environmental-induced modifications, which can lead to deleterious or catastrophic consequences. This is increasingly important as small satellites—with minimal shielding due to reduced mass and size constraints and reliance on more compact and sensitive electronics—have longer mission lifetimes and make more diverse, complex and sensitive measurements. The current push to expand deployment of CubeSats beyond LEO, into even more demanding environments where modest relief due to shielding by the Earth’s magnetosphere is absent (such as polar or GEO orbits), can further exacerbate these problems.

Testing of small satellites is therefore critical to avoid such problems. A …

Photonicstd-2d: Modeling Light Scattering In Periodic Multilayer Photonic Structures, Alexey Bondarev, Shaimaa Azzam, Zhaxylyk Kudyshev, Alexander V. Kildishev

The Summer Undergraduate Research Fellowship (SURF) Symposium

Efficient modeling of electromagnetic processes in optical and plasmonic metamaterials is important for enabling new and exciting ways to manipulate light for advanced applications. In this work, we put together a tool for numerical simulation of propagation of normally incident light through a nanostructured multilayer composite material. The user builds a unit cell of a given material layer-by-layer starting from a substrate up to a superstrate, splitting each layer further into segments. The segments are defined by width and material -- dielectric, metal or active medium. Simulations are performed with the finite difference time domain (FDTD) method. A database of …

Classifying Pattern Formation In Materials Via Machine Learning, Lukasz Burzawa, Shuo Liu, Erica W. Carlson

The Summer Undergraduate Research Fellowship (SURF) Symposium

Scanning probe experiments such as scanning tunneling microscopy (STM) and atomic force microscopy (AFM) on strongly correlated materials often reveal complex pattern formation that occurs on multiple length scales. We have shown in two disparate correlated materials that the pattern formation is driven by proximity to a disorder-driven critical point. We developed new analysis concepts and techniques that relate the observed pattern formation to critical exponents by analyzing the geometry and statistics of clusters observed in these experiments and converting that information into critical exponents. Machine learning algorithms can be helpful correlating data from scanning probe experiments to theoretical models …

Hydrogel Microphones For Stealthy Underwater Listening, Yang Gao, Jingfeng Song, Shumin Li, Christian Elowsky, You Zhou, Stephen Ducharme, Yong Mei Chen, Qin Zhou, Li Tan

Stephen Ducharme Publications

Exploring the abundant resources in the ocean requires underwater acoustic detectors with a high-sensitivity reception of low-frequency sound from greater distances and zero reflections. Here we address both challenges by integrating an easily deformable network of metal nanoparticles in a hydrogel matrix for use as a cavity-free microphone. Since metal nanoparticles can be densely implanted as inclusions, and can even be arranged in coherent arrays, this microphone can detect static loads and air breezes from different angles, as well as underwater acoustic signals from 20 Hz to 3 kHz at amplitudes as low as 4 Pa. Unlike dielectric capacitors or …

Localization And Delocalization In Two-Dimensional Quantum Percolation, Brianna S. Dillon Thomas

Open Access Dissertations

Quantum percolation is one of several disorder-only models that address the question of whether conduction, or more generally, delocalization, is possible in two dimensional disordered systems. Whether quantum percolation exhibits a delocalization-localization phase transition in two dimensions is an ongoing debate, but many recent studies point toward there being a delocalized phase at non-zero disorder, in contradiction to the behavior of the Anderson model, another disorder-only model. In this dissertation, I present my research on quantum percolation that shows a delocalized state is possible, both on isotropic lattices and on highly anisotropic lattices, and shows that the essential characteristics of …

Probing Symmetry And Disorder Effects In The Fractional Quantum Hall States Of The Second Landau Level, Ethan I. Kleinbaum

Open Access Dissertations

Electrons confined to two dimensions, cooled to cryogenic temperatures, and placed in a strong perpendicular magnetic field exhibit a set of ground states referred to as the fractional quantum Hall states (FQHS). The FQHSs forming in the region called the second Landau level are some of the most exciting states as several theories predict that they are very different from the well understood FQHS in the lowest Landau level. Nonetheless, the nature of these FQHSs continue to evade understanding. In this thesis, a unique ultra-low temperature setup is used to examine the FQHSs of the second Landau level in regimes …

Metal Semiconductor Contact Between Gold And Boron Carbide, Ethiyal Raj Wilson, Elena Echeverria, Aiyun Liu, Bin Dong, George Peterson, Michael Nastasi, Peter A. Dowben

UCARE: Research Products

We have investigated the interaction of gold (Au) with the semiconductor boron carbide through X-ray photoemission and heterojunction diode fabrication. The plasma enhanced chemical vapor deposition (PECVD) hydrogenated semiconducting boron carbide films, deposited from closo-1,7-dicarbadodecaborane (metacarborane, m-B₁₀C₂H₁₂), shows a shift in the binding energies of the core level photoemission features when gold is deposited on the surface. The shifting of the B 1s level is smaller than for the C 1s level and the non-uniform nature of the shifts indicates a strong, complex and reversible gold chemical interaction with the surface, particularly with the …

Low-Dimensional Materials For Organic Electronic Applications, Sumit Beniwal

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

This thesis explores the self-assembly, surface interactions and electronic properties of functional molecules that have potential applications in electronics. Three classes of molecules - organic ferroelectric, spin-crossover complex, and molecules that assemble into a 2D semiconductor, have been studied through scanning tunneling microscopy and surfacesensitive spectroscopic methods. The scientific goal of this thesis is to understand the self-assembly of these molecules in low-dimensional (2D) configurations and the influence of substrate on their properties. First, a H-bonded organic ferroelectric, the 3-Hydroxyphenalenone, is studied on two noble metal substrates. It is demonstrated how a variety of different assemblies including 1D chains, p-p …

Materials Design And Band Gap Engineering Of Complex Nanostructures Using A Semi-Empirical Approach : Low Dimensional Boron Nanostructures, H-Bn Sheet With Graphene Domains And Holey Graphene., Cherno Baba Kah

Electronic Theses and Dissertations

This dissertation will explore the potential of a semi-empirical Hamiltonian, developed by the research group at the University of Louisville, in predicting the existence of new families of low-dimensional boron nanostructures based on icosahedral α-B₁₂ clusters, and in tuning the band gaps of h-BN sheets with graphene domains and holey graphene. This semi-empirical Hamiltonian models electron-electron and electron-ion interactions using environment-dependent (ED) functions, and ion-ion interactions via usual pairwise terms. Additional features of our approach are that it uses a linear combination of atomic orbitals (LCAO) framework to describe the Hamiltonian and it calculates the charge distribution around a …

Spica: Stereographic Projection For Interactive Crystallographic Analysis, Xingzhong Li

Nebraska Center for Materials and Nanoscience: Faculty Publications

In numerous research fields, especially the applications of electron and X-ray diffraction, stereographic projection represents a powerful tool for researchers. SPICA is a new computer program for stereographic projection in interactive crystallographic analysis, which inherits features from the previous JECP/SP and includes more functions for extensive crystallographic analysis. SPICA provides fully interactive options for users to plot stereograms of crystal directions and crystal planes, traces, and Kikuchi maps for an arbitrary crystal structure; it can be used to explore the orientation relationships between two crystalline phases with a composite stereogram; it is also used to predict the tilt angles of …

Preparation And Characterization Of Van Der Waals Heterostructures, Horacio Coy Diaz

USF Tampa Graduate Theses and Dissertations

In this dissertation different van der Waals heterostructures such as graphene-MoS₂ and MoTe₂-MoS₂ were prepared and characterized. In the first heterostructure, polycrystalline graphene was synthesized by chemical vapor deposition and transferred on top of MoS₂ single crystal. In the second heterostructure, MoTe₂ monolayers were deposited on MoS₂ by molecular beam epitaxy.

Characterization of graphene-MoS₂ heterostructures was conducted by spin and angle resolve spectroscopy which showed that the electronic structure of the bulk MoS₂ and graphene in this van der Waals heterostructures is modified. For MoS₂ underneath the graphene, a band …

Simultaneous Metal-Insulator And Antiferromagnetic Transitions In Orthorhombic Perovskite Iridate Sr0.94Ir0.78O2.68 Single Crystals, Hao Zheng, Jsaminka Terzic, Feng Ye, X. G. Wan, D. Wang, Jinchen Wang, Xiaoping Wang, P. Schlottmann, Shujuan Yuan, Gang Cao

Center for Advanced Materials Faculty Publications

The orthorhombic perovskite SrIrO₃ is a semimetal, an intriguing exception in iridates where the strong spin-orbit interaction coupled with electron correlations tends to impose an insulating state. We report results of our investigation of bulk single-crystal S_r0.94Ir_0.78O_2.68 or Ir-deficient, orthorhombic perovskite SrIrO₃. It retains the same crystal structure as stoichiometric SrIrO₃ but exhibits a sharp, simultaneous antiferromagnetic (AFM) and metal-insulator (MI) transition occurring in the basal-plane resistivity at 185 K. Above it, the basal-plane resistivity features an extended regime of almost linear temperature dependence up to 800 K but the strong …

Anisotropic Softening Of Magnetic Excitations In Lightly Electron-Doped Sr2Iro4, X. Liu, M. P. M. Dean, Z. Y. Meng, M. H. Upton, T. Qi, T. Gog, Y. Cao, J. Q. Lin, D. Meyers, H. Ding, Gang Cao, J. P. Hill

Center for Advanced Materials Faculty Publications

The magnetic excitations in electron-doped (Sr_1−xLa_x)₂IrO₄ with x = 0.03 were measured using resonant inelastic x-ray scattering at the Ir L₃ edge. Although much broadened, well defined dispersive magnetic excitations were observed. Comparing with the magnetic dispersion from the undoped compound, the evolution of the magnetic excitations upon doping is highly anisotropic. Along the antinodal direction, the dispersion is almost intact. On the other hand, the magnetic excitations along the nodal direction show significant softening. These results establish the presence of strong magnetic correlations in electron-doped (Sr_1−xLa_{x …}

Transport Of Dirac Electrons In A Random Magnetic Field In Topological Heterostructures, Hilary M. Hurst, Dimitry K. Efimkin, Victor Galitski

Faculty Research, Scholarly, and Creative Activity

We consider the proximity effect between Dirac states at the surface of a topological insulator and a ferromagnet with easy plane anisotropy, which is described by the XY model and undergoes a Berezinskii-Kosterlitz-Thouless (BKT) phase transition. The surface states of the topological insulator interacting with classical magnetic fluctuations of the ferromagnet can be mapped onto the problem of Dirac fermions in a random magnetic field. However, this analogy is only partial in the presence of electron-hole asymmetry or warping of the Dirac dispersion, which results in screening of magnetic fluctuations. Scattering at magnetic fluctuations influences the behavior of the surface …

Classical Transport In Disordered Systems, Antonios Papaioannou

Dissertations, Theses, and Capstone Projects

This thesis reports on the manifestation of structural disorder on molecular transport and it consists of two parts. Part I discusses the relations between classical transport and the underlying structural complexity of the system. Both types of molecular diffusion, namely Gaussian and non-Gaussian are presented and the relevant time regimes are discussed. In addition the concept of structural universality is introduced and connected with the diffusion metrics. One of the most robust techniques for measuring molecular mean square displacements is magnetic resonance. This method requires encoding and subsequently reading out after an experimentally controlled time, a phase ϕ to the …

Effect Of Electrolyte Concentration On The Capacitance And Mobility Of Graphene, Flint A. Martino

Senior Theses

The use of graphene field-effect transistors as a biosensor is increasingly being used to study biological phenomena, due to the sensitivity and low reactivity of graphene. To further improve sensitivity in biological environments, we examined how different salt concentrations affect the mobility of capacitance of the graphene. Samples were also measured after an annealing process. We report on the positive correlation between sensitivity and electrolyte concentration and speculate on methods to improve future detectors. Mobility of the device was found to change from 1.07*10³cm²/ (V*s) in de-ionized water to 2.78*10³cm²/ (V*s) in …