Bulletin of the American Physical Society
82nd Annual Meeting of the APS Southeastern Section
Volume 60, Number 18
Wednesday–Saturday, November 18–21, 2015; Mobile, Alabama
Session D2: Condensed Matter Physics II |
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Chair: Anota Ijaduola, University of North Georgia Room: Riverview Plaza Hotel Mobile Bay Ballroom I |
Thursday, November 19, 2015 2:45PM - 2:57PM |
D2.00001: Terahertz time-domain reflection spectroscopy of the insulator-to-metal phase transition in vanadium dioxide Aidan O'Beirne, Luke McClintock, Jeremy Curtis, Richard Haglund, David Hilton Terahertz time-domain spectroscopy is a well-established experimental technique that is commonly used to determine the complex dielectric constants of condensed matter systems. This experiment typically measure samples in transmission since the analysis methods for reflection geometry have well known phase ambiguities that cannot easily be overcome. This is a significant limitation since materials with strong absorption can often be studied only in reflection and also because some experimental geometries, like the high field magnets at NHMFL, only permit reflection measurements. To develop a new terahertz reflection spectroscopy method, we have performed terahertz time-domain spectroscopy of vanadium dioxide ($\mathrm{VO_2}$), which exhibits a insulator-to-metal phase transition at 340 K, as a function of temperature in a novel reflection geometry that includes a second reference beam to overcome the prior phase ambiguities. Our analysis uses the Characteristic matrix method to determine the complex dielectric constants as a function of temperature, which we have measured between 315 K to 365 K and then back to 315 K. We have obtained the complex conductivity of this $\mathrm{VO_2}$ sample, which agrees with the known conductivity hysteresis of this material. [Preview Abstract] |
Thursday, November 19, 2015 2:57PM - 3:09PM |
D2.00002: Effects of substrate on the superconducting properties and ferromagnetic loss in RABiTS coated conductors Anota Ijaduola, C. L. H. Thieme, M. W. Rupich, A. Goyal Given the substantial progress in the fabrication of coated conductors, considerable attention is now being directed to studying and understanding the ferromagnetic loss that arise from the substrates. Rolling Assisted Biaxially Textured Substrates (RABiTS) coated conductors (CC) use alloys of NiW as the preferred substrate during fabrication. In this work, we have made magnetic measurements on a set of RABiTS CC with different composition of NiW alloy in order to determine the amount of ferromagnetic loss from the substrates. We also report on the magnetometric studies of the critical current density $J_c$ flowing in the thin $YBa_2Cu_3O_{7-\delta}$ (YBCO) films that were deposited on these substrates. The $J_c$ were determined both as a function of applied field $H$ and temperature $T$. Isothermal magnetization loops $M(H; T)$ and remanent magnetization $M_{rem} (T)$ in zero applied field $H = 0$, were measured with $H$ parallel to the c axis (i.e., normal to film plane). For a wide range of temperatures and intermediate fields, we find a power law falloff $J_c \propto H^{-\beta}$ with $\beta$ $\sim$ (0.56 - 0.69) for all materials. For higher temperatures approaching the irreversibility line, we find $J_c (T, sf) \propto (1-T/Tc)^n$ with n $\sim$ 1.1 - 1.3. [Preview Abstract] |
Thursday, November 19, 2015 3:09PM - 3:21PM |
D2.00003: HEAVIER-THAN-TARGET SURFACE SCATTERING Dhruva Kulkarni, Chad Sosolik We have measured the scattering of hyperthermal Cs$^{\mathrm{+}}$ ions (m$=$132.9u) incident at 45$^{\mathrm{o\thinspace }}$and 60$^{\mathrm{o}}$ to the surface of a Cu (0 0 1) (m$=$63.5u) crystal. Energy resolved spectra were measured for a range of angles about the specular angle in the forward direction. Deviation from standard spectra, typically interpreted as binary collisions, is observed due to the projectile-heavier-than-target nature of scattering. The measured spectra can be interpreted as collective events that are more pronounced due to an inverted mass ratio. Linear relationships in perpendicular and parallel ``components'' of energy loss at the two different incident angles help identify scattering events that lead to reflection of heavy atoms from the surface. [Preview Abstract] |
Thursday, November 19, 2015 3:21PM - 3:33PM |
D2.00004: Distribution of Impurities in Lithium Niobate Chandrima Chatterjee, Igor Ostrovskii The functional parameters of LiNbO$_{\mathrm{3}}$ in various acousto-opto-electronic applications are questionable. The nonclassical nonlinear effect such as ``acoustical memory'' is hardly explained. The present research aims to find new crystal characteristics including the identification of impurities and point defects along the optical crystallographic Z-axis, and normal to the Z-axis. The bulk crystals and wafers are studied. The impurities are identified by their characteristic lines in the photoluminescence spectra, which are taken at room temperature in a range of 350 to 900 nm. The spectra reveal the following point defects: Ar, Ba, Cs, F-center, Rb, Ru, Sn, Fe, K, Li, O, Nb, Kr Nb$_{\mathrm{Li}}^{\mathrm{4+}}$, Xe, etc. The peak corresponding to the F-center is found at 400.429 nm and has the highest number of photon counts. The samples are shifted with a step of tens of microns along the Z-axis or normal to it. This allows to find a distribution of the impurities in the samples. The photon counts change with crystal position for some impurities. The distribution of these defects is observed as peaks and valleys. The results may be used to discover the physical mechanisms behind nonclassical nonlinear phenomena in LiNbO$_{\mathrm{3}}$. [Preview Abstract] |
Thursday, November 19, 2015 3:33PM - 3:45PM |
D2.00005: \textbf{CO Adsorption on Pd(111) at 0.5ML: a First Principles Study} Zahra Hooshmand Gharehbagh, Duy Le, Talat Rahman While the overlayer structures formed by CO molecules on Pd(111) are well-understood both experimentally and theoretically for low and high coverages, it is still a matter of discussion for medium coverage (0.5ML). At this coverage, it is well-known that the c(4 \begin{figure}[htbp] \centerline{\includegraphics[width=0.10in,height=0.17in]{161020151.eps}} \label{fig1} \end{figure} 2) phase is formed but the adsorption sites of CO molecules have been reported differently by various studies: at the bridge sites, at the hollow sites, or at both bridge and hollow sites. Using density functional theory calculations we studied the overlayer structure of CO at 0.5ML on Pd(111) with all possible highly symmetric adsorption sites leading to c(4 \begin{figure}[htbp] \centerline{\includegraphics[width=0.10in,height=0.17in]{161020152.eps}} \label{fig2} \end{figure} 2) structures. We will show that CO molecules adsorb only on hollow sites and that there is no overlayer structure in which CO binds at both bridge and hollow sites or bridge sites only. By simulating Scanning Tunneling Microscopy (STM) images of obtained structures we could predict the one corresponding to the most frequently observed STM and correctly assign the experimental STM images to CO overlayer structures. [Preview Abstract] |
Thursday, November 19, 2015 3:45PM - 3:57PM |
D2.00006: New Indexing Method for Zinc Blende Crystals: Applied to Kinetic Monte Carlo Simulations Kyle Bentley, Ryoichi Kawai Usual methods of indexing a zinc blende, or diamond cubic lattice with Cartesian coordinates is cumbersome to use in Monte Carlo simulations with fixed-length step sizes. There is to date no method of quickly gathering information about specific neighboring atoms that isn't costly in terms of computational time. We have shown that a simplified method of indexing a zinc blende and diamond cubic lattice can reduce the complexity of simulations, while at the same time increase computational performance. These methods prove useful in modeling the diffusion of native defects and dopants in binary compound systems, such as chalcogenide, oxide, and nitride systems, as well as diamond, silicon, germanium, and many others. Utilizing these algorithms we are able to simulate diffusion time scales in the microsecond regime in a reasonable amount of time. We will show kinetic Monte Carlo simulations of diffusion in zinc oxide crystals. [Preview Abstract] |
Thursday, November 19, 2015 3:57PM - 4:09PM |
D2.00007: Critical Initial Slip Scaling for Driven-dissipative Bose-Einstein Condensation Weigang Liu The universal critical behavior near the continuous non-equilibrium phase transition of driven-dissipative Bose gases is investigated employing the perturbative field-theoretic renormalization group method. Such criticality may be realized in a broad range of driven open systems on the interface of quantum optics and many-body physics, ranging from exciton--polariton condensates to cold atomic gases. The starting point is a noisy, dissipative Gross-Pitaevski equation corresponding to a complex-valued Landau-Ginzburg functional, which captures the near critical non-equilibrium dynamics, as well as a Gaussian weighted random initial state, which breaks time translation invariance. This setup generalizes the standard equilibrium Model A kinetics for classical relaxational dynamics with non-conserved order parameter. We study the universal critical behavior of this system in the early stages of the relaxation process, which is governed by an independent so-called initial-slip exponent. To one-loop order in the dimensional expansion about the upper critical dimension, this initial slip exponent is identical to its equilibrium counterpart. We argue that this remains likely true to all orders in the perturbation expansion. This research is supported by the U. S. Department of Energy, Office of Basic Energy Sciences, Division of Materials Science and Engineering under Award DE-FG02-09ER46613. [Preview Abstract] |
Thursday, November 19, 2015 4:09PM - 4:21PM |
D2.00008: Comprehensive theory of deformation and fracture Sanichiro Yoshida Based on the principle of local symmetry applied to Hooke's law, deformation and fracture of solids are being theorized in a comprehensive fashion. Allowing coordinate dependence in the transformation matrix representing local linear elasticity and requesting that the dynamics be described at the global level in the same form as the local level, a connection field is introduced. With the use of the Lagnrangian formalism, a set of field equations are derived. The field equations yield wave solutions that represent wave dynamics of deformation of all regimes. Dynamics of different regimes can be differentiated as difference in the mechanism of longitudinal recovery force. Elastic deformation is characterized by a longitudinal wave associated with longitudinal spring force; plastic deformation is characterized by a decaying transverse wave associated with transverse (shear) recovery force and longitudinal damping force; and elasto-plastic deformation is characterized by a solitary wave resulting from a combination of the elastic and plastic dynamics. Experiments have been conducted with the use of optical interferometry to measure the displacement field of specimens under tensile loads. Wave dynamics of all the regimes have been observed experimentally. [Preview Abstract] |
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