Bulletin of the American Physical Society
APS March Meeting 2010
Volume 55, Number 2
Monday–Friday, March 15–19, 2010; Portland, Oregon
Session Z15: Structural and Electronic Properties of Metals II |
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Sponsoring Units: DCMP Chair: T. Hickel, Max-Planck Institut fur Eisenforschung Room: B114 |
Friday, March 19, 2010 11:15AM - 11:27AM |
Z15.00001: Bonding in boron: building high-pressure phases from boron sheets Jens Kunstmann, Lilia Boeri, Jens Kortus We present the results of a study of the high pressure phase diagram of elemental boron, using full-potential density functional calculations. We show that at high pressures (P > 100 GPa) boron crystallizes in quasi-layered bulk phases, characterized by in-plane multicenter bonds and out-of-plane unidimensional sigma bonds. These structures are all metallic, in contrast to the low-pressure icosahedral ones, which are semiconducting. We show that the structure and bonding of layered bulk phases can be easily described in terms of single puckered boron sheets [1]. Our results bridge the gap between boron nanostructures and bulk phases.\\[4pt] [1] Kunstmann et al., Phys. Rev. B 74, 035413 (2006). [Preview Abstract] |
Friday, March 19, 2010 11:27AM - 11:39AM |
Z15.00002: Phonon dispersion relations in cerium under pressure across the volume-collapse gamma-alpha transition Michael Krisch, Daniel Farber, R. Xu, D. Antonangeli, C. Aracne, A. Beraud, T.-C. Chiang Cerium is a rare-earth metal with many of its physical and chemical properties governed by the complex behavior of its 4f electron in contributing to the bonding of the crystal structure. Specifically, its gamma-alpha volume-collapse transition under pressure is the only known solid-solid transition in an element with the phase boundary ending at a critical point, and the detailed mechanism is still not fully understood. We report recent inelastic x-ray scattering measurements of phonon dispersion relations of cerium at room temperature as a function of pressure up to 25 kbar. The phonon dispersion relations show abrupt changes across the gamma-alpha transition at $\sim $7 kbar and continue to evolve at higher pressures. Various thermodynamic quantities associated with the transition are deduced. These results will be discussed in light of existing theories and models. [Preview Abstract] |
Friday, March 19, 2010 11:39AM - 11:51AM |
Z15.00003: Nonlinear Surface Plasmon Polariton Propagation and Third Harmonic Generation at a Planar Metal/Dielectric Interface Yan Guo, Miriam Deutsch Surface plasmon polaritons (SPPs) are electromagnetic (EM) waves guided at the interface between a metal and a dielectric. The confinement of EM fields to practically two dimensions leads to extremely high energy densities at the interface. We consider here the interaction of such optical fields with noble metals possessing large third order hyperpolarizabilities. We present analytical solutions to the nonlinear Maxwell equations with third order optical susceptibility. Surface electric dipoles induced at the metal/dielectric interface induce a third harmonic EM wave whose frequency lies above the plasma edge of the metal. The induced field thus becomes a leaky mode, guided at the air-side of the interface while freely propagating into the metal. Various necessary approximations, their limitations and implications are also discussed. [Preview Abstract] |
Friday, March 19, 2010 11:51AM - 12:03PM |
Z15.00004: Measurements of higher-order moments of the persistent current in normal metal rings Will Shanks, Ania Bleszynski Jayich, Bruno Peaudecerf, Eran Ginossar, Leonid Glazman, Felix von Oppen, Jack Harris A normal metal ring exhibits a persistent electrical current provided its circumference is less than the electron's phase coherence length and its temperature is less than the Thouless temperature. The amplitude of the persistent current is a random function of the ring's disorder configuration. To date, theory and experiments have focused on measuring the variance of the distribution from which the persistent current amplitude is drawn. We have measured persistent currents in arrays of normal-metal rings over a wide range of magnetic fields, or equivalently, over many independent realizations of the disorder potential. This data allows us to produce a histogram of the current amplitude and determine its higher order moments. We find these higher order moments are consistent with a Gaussian distribution for the persistent currents. We also directly confirm that the amplitudes of different harmonics of the currents' Aharonov-Bohm oscillations are uncorrelated. [Preview Abstract] |
Friday, March 19, 2010 12:03PM - 12:15PM |
Z15.00005: Anisotropic Rashba splitting of Au(110) surface states Balazs Ujfalussy, Eszter Simon, Attila Szilva, Gergely Zarand, Bence Lazarovits, Laszlo Szunyogh We investigate the surface Rashba effect subject to reduced in-plane symmetry. Based on a \textbf{K.p} perturbation theory, we give a detailed microscopic description of the Anisotropic Rashba Splitting (ARS). Furthermore, we show that this ARS can not be explained within the standard theoretical picture of the Rashba effect assuming a purely normal-to-surface variation of the crystal potential. The new microscopic expression for the Rashba Hamiltonian is explicitelly supported by fully relativistic first principles calculations for the case of unreconstructed Au(110) surface. [Preview Abstract] |
Friday, March 19, 2010 12:15PM - 12:27PM |
Z15.00006: Strain-induced metal-hydrogen interactions across the first transition series -- An \textit{ab initio} study of hydrogen embrittlement Johann von Pezold, Ugur Aydin, J\"org Neugebauer The attractive interaction between hydrogen and distorted regions of the host matrix underlies all the currently discussed mechanisms of hydrogen-induced embrittlement of metals, such as hydrogen enhanced local plasticity (HELP), hydrogen enhanced decohesion (HEDE) and stress-induced hydride formation. In this study we investigate these interactions systematically by determining heat of solutions, H-H binding energies within the metal matrix, as well as phase diagrams as a function of the lattice strain and the H chemical potential across the first transition series (3d elements) using Density Functional Theory (DFT) calculations. The results will be interpreted in terms of the likely embrittlement mechanisms of these metals. [Preview Abstract] |
Friday, March 19, 2010 12:27PM - 12:39PM |
Z15.00007: Ab initio determination of the magnetic free energy contribution of metallic systems Fritz K\"ormann, Alexey Dick, Blazej Grabowski, Tilmann Hickel, J\"org Neugebauer An accurate prediction of the free energy is the basis to compute phase diagrams, finite temperature materials parameters, or kinetic barriers and is thus fundamental in computational materials design. One of the most challenging contributions - but crucial for many engineering materials - is the magnetic entropy. The most popular ab initio approach for the latter is the use of an effective Heisenberg model solved using classical Monte Carlo (cMC) approaches and neglecting quantum effects. We discuss the impact of the latter based on extensive model calculations where Quantum MC calculations are available. An empirical rescaling scheme is derived allowing to considerably improve the cMC. The method is applicable to strong ferromagnetic systems with magnetic frustration is absent or weak. The application and performance of the new approach is demonstrated for pure Fe. [Preview Abstract] |
Friday, March 19, 2010 12:39PM - 12:51PM |
Z15.00008: Tuning Magnetic Interactions in a Two Dimensional Matrix Timothy Kidd, Michael Roth, Paul Shand, Tyler Rash, Laura Strauss, Brodie Wandling The layered dichalcogenides can be used as a matrix for incorporating and manipulating dopants in dimensionally constrained manner. The crystal structure of the dichalcogenides is formed of two-dimensional strongly bound layers separated by a van der Waals gap. Dopants can be incorporated between the layers as intercalants through a variety of methods to form semi-ordered phases. These intercalants have a strong impact on the electronic and magnetic properties of the overall system and can be used to tune existing or induce new phase transitions in the pure parent compounds. For magnetic intercalants, RKKY interactions, which have a strong dependence on the ion-ion spacing, appear to determine the overall magnetic character of the system. Herein, we discuss how Coulomb interactions between intercalated magnetic and non-magnetic ions can be used to influence the spacing between magnetic species and drastically alter the overall magnetic properties of the system. [Preview Abstract] |
Friday, March 19, 2010 12:51PM - 1:03PM |
Z15.00009: Kapitza Resistance at the Solid-Liquid Interface Sanghamitra Neogi, Gerald Mahan We study the thermal boundary resistance between the electrons in a metal and the phonons in a liquid. The theory includes transverse modes in the fluid that can carry diffusive heat from the interface into the bulk of the liquid. The theory can be an extension over the acoustic mismatch theory for Kapitza resistance. [Preview Abstract] |
Friday, March 19, 2010 1:03PM - 1:15PM |
Z15.00010: Quantifying Uncertainty in Materials Properties from Microstructure Variability Corbett Battaile, Luke Brewer, Brad Boyce, John Emery Most materials are inherently inhomogeneous. This means that their internal structure varies from point to point on the microscale; from region to region on the macroscale; from part to part; and throughout time as they age. Because a material's microstructure often controls its properties, the variability in structure leads to uncertainty about the material's properties and performance. We will discuss the concept of a statistics-based treatment of the process-structure-properties-performance relationships in engineering materials, and describe both experiments and computational simulations designed to quantify the statistics underlying structure-properties relationships in poly-silicon MEMS devices, stainless steel welds, and alpha-brass with engineered defects. [Preview Abstract] |
Friday, March 19, 2010 1:15PM - 1:27PM |
Z15.00011: Low-energy behavior near the semi-Dirac point Swapnonil Banerjee, W.E. Pickett The recent discovery that a three unit cell slab of VO$_2$ confined to 2D dispersion within insulating TiO$_2$ slabs leads to point Fermi surfaces [PRL 102, 166803 (2009)] has opened up a new class of electronic behavior. It shows four symmetry related point Fermi surfaces along the (1,1) directions in the 2D Brillouin zone. The dispersion away from this point is however different from graphene and was unanticipated: disperson is linear along one direction but quadratic in the perpendicular direction. This semi-Dirac behavior has extreme anisotropy, from massless to massive. The dispersion depends on the Fermi velocity $v_F$ and the effective mass $m^*$, but finally scales to a single semi-Dirac system with energy scale $m^* v_F^2$. We have extended the study of the low energy behavior of this system [PRL 103, 016402 (2009)], showing that the Hall coefficient reduces to the conventional expression $\frac{1}{nec}$ ($n$ is the carrier concentration) as also the case for graphene, but does not hold generally. The small-q electronic response and plasmon frequency, and its very strong anisotropy, will be presented and analyzed. [Preview Abstract] |
Friday, March 19, 2010 1:27PM - 1:39PM |
Z15.00012: Construction of Chiral Metamaterial with U-Shaped Resonator Assembly Xiang Xiong, Wei-Hua Sun, Yong-Jun Bao, Ru-Wen Peng, Mu Wang, Cheng Sun, Xiang Lu, Jun Shao, Zhi-Feng Li, Nai-Ben Ming Chiral structure can be applied to construct metamaterial with negative refractive index (NRI). In an assembly of double-layered metallic U-shaped resonators with two resonant frequencies $\omega _{H}$ and $\omega _{L}$, the effective induced electric and magnetic dipoles, which are contributed by the specific surface current distributions, are collinear at the same frequency. Consequently, for left circularly polarized light, NRI occurs at \textit{$\omega $}$_{H}$ , whereas for right circularly polarized light it occurs at \textit{$\omega $}$_{L}$. Our design provides a new example to apply chiral structures to tune electromagnetic properties, and could be enlightening in exploring chiral metamaterials. [Preview Abstract] |
Friday, March 19, 2010 1:39PM - 1:51PM |
Z15.00013: Field-Biased Molecular Simulation Technique for Polyelectrolytes Amir Vahid, J. Richard Elliott External fields can be used to impose density profiles in inhomogeneous fluids and interfacial phenomena1. In this study an electric field has been imposed on 1372 hard spheres through 20 negative point charges and 20 positive charges. Also, the effect of partial charges was investigated on a polyelectrolyte with implicit and explicit solvent. Long-range interactions are considered through particle-mesh Ewald summation and its pairwise alternatives. It has been found that it is not necessary to update the Coulombic interactions after each time-step. Energy is conserved even after many numbers of time-steps. Therefore, the computation time for the long-range interaction is less than the discontinuous molecular dynamic (DMD) and/or discontinuous Monte Carlo components. This means that the forced-biased discontinuous molecular simulation method is viable for future studies of confined fluids containing interface and ionic liquids as performed with a field-biased conventional molecular dynamic method by Wardle et al. Finally, the effect of the biased method on dihedral angle is investigated. [Preview Abstract] |
Friday, March 19, 2010 1:51PM - 2:03PM |
Z15.00014: Point defects in In$_2$O$_3$ Kalum Palandage, Gayanath Fernando Point defects in $In_2O_3$ were studied using first principles, density functional theory within the local density /local spin density approximation. New results will be reported about the conductivity and magnetism, arising from these point defects. Various systematic corrections were performed to check the validity of the results. [Preview Abstract] |
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