Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session L28: Phonons in Metals |
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Sponsoring Units: DMP Chair: Adolfo Equiluz, University of Tennessee Room: LACC 506 |
Tuesday, March 22, 2005 2:30PM - 2:42PM |
L28.00001: A Study of the Cross--Over Temperature between the Adiabatic and Non--Adiabatic Contributions to the Electron--Phonon Free Energy in Na, K, Al, and Pb Nicolas Bock, Dermot Coffey, Duane Wallace We calculate the electron--phonon contribution to the free energy and entropy for four elemental metals, Na, K, Al, and Pb, using realistic phonon spectra and pseudopotentials for temperatures between $0 \leq T < 1.5 \,\, T_{melt}$. We show that the non--adiabatic contribution dominates at low temperatures whereas the adiabatic contribution dominates at high temperatures. We calculate the cross--over temperatures between the two contributions which is roughly between 0.5 and 0.8 $T_{melt}$. Where we are able to compare, we find good agreement with experiment. [Preview Abstract] |
Tuesday, March 22, 2005 2:42PM - 2:54PM |
L28.00002: Calculation of phonon dispersion relations and softening in photo-excited bismuth Eamonn Murray, Stephen Fahy The phonon dispersion relations for equilibrium and photo-excited bismuth are calculated using density functional theory, combined with constrained density functional theory. The dependence of phonon frequency on photo-excited electron-hole plasma density is found for modes throughout the Brillouin Zone. The results are in excellent agreement with available neutron scattering data for the equilibrium occupation of electronic bands. We find the effect of phonon softening by the electron-hole plasma to be larger in the optical modes than in the acoustic modes. [Preview Abstract] |
Tuesday, March 22, 2005 2:54PM - 3:06PM |
L28.00003: Compositional variation of the phonon dispersion curves of bcc Fe-Ga alloys J.L. Zarestky, V.O. Garlea, T.A. Lograsso, D.L. Schlagel, C. Stassis Inelastic neutron scattering techniques have been used to measure the phonon dispersion curves of bcc Fe-Ga alloys as a function of Ga concentration. We observed that the phonon frequencies of every branch decrease significantly with increasing Ga concentration with the softening being more pronounced for the T$_{2}$[110] branch and for the L[111] in the vicinity of $\xi $ = (2/3, 2/3,2/3). The slope of the T$_{2}$[110] branch was found to decrease linearly with increasing Ga concentration and to extrapolate to zero at approximately 27 at.{\%} in agreement with the results of sound velocity measurements. As the Ga concentration increases, a splitting of the T$_{1}$[110] branch is observed, an effect characteristic of diatomic lattices. [Preview Abstract] |
Tuesday, March 22, 2005 3:06PM - 3:18PM |
L28.00004: First-principles elastic constants and phonons of $\delta$-Pu Per S\"oderlind, Alex Landa, Babak Sadigh Elastic constants and zone boundary phonons of $\delta$-Pu have been calculated within the density-functional theory. The electronic structure is modeled by disordered magnetism utilizing either the disordered local moment or the special quasi-random structure techniques. The anomalously soft C$^ {prime}$ as well as a large anisotropy ratio of $\delta$-Pu is reproduced by this first-principles model. Also the measured phonons for $\delta$-Pu compare relatively well with their theoretical counterpart at the zone boundary. [Preview Abstract] |
Tuesday, March 22, 2005 3:18PM - 3:30PM |
L28.00005: Phonon Entropy of Alloying in Dilute Vanadium Alloys Olivier Delaire, Tabitha Swan-Wood, Max Kresch, Brent Fultz We investigate the entropic effects associated with changes in the phonon modes of vanadium upon dilute substitutional alloying. Using inelastic neutron scattering, we have measured the phonon DOS and the phonon entropy of mixing in V - 6\%X, with X a transition metal impurity. We study trends for impurities across the d-series and down several columns of the periodic table. We show that for Ni, Pd and Pt impurities, the phonon entropy of alloying is large and negative, and in the case of Pt it results in a negative total entropy of mixing for 6\% impurities. A Born-von Karman model was used to invert the experimental DOS curves and showed that the phonon stiffening down this column is associated with an increases in 1NN longitudinal inter-atomic force-constants. The changes in the phonon DOS for impurities across the 3d series are also correlated with the previously measured changes in the superconducting temperature $T_{c}$. Ab-initio DFT simulations were used to compute the effect of impurities on the electronic and phonon properties of vanadium, and are compared to the experimental results. This work was supported by DOE through the BES Grant DE-FG03-0346055 and BES-MS, W-31-109-ENG-38. [Preview Abstract] |
Tuesday, March 22, 2005 3:30PM - 3:42PM |
L28.00006: Ultrasonic study of $Gd_{5}(Si_{2}Ge_{2})$ elastic properties O. Svitelskiy, A. Suslov, T.A. Lograsso, D.L. Schlagel, V.K. Pecharsky, K.A. Gschneidner, Jr. $Gd_{5}(Si_{2}Ge_{2})$ undergoes a magnetic-martensitic transition near room temperature modifying its symmetry from an orthorhombic to a monoclinic structure. A giant magnetocaloric effect ($\Delta T/\Delta B\sim 8K/2T$) and a colossal strain (up to 10000ppm) can be induced both thermally and magnetically. Due to low hysteresis ($<$2K,$<$0.5T), the material has a potential for energy efficient refrigeration and actuation uses. The acoustic phonon properties of the $Gd_{5}(Si_{2}Ge_{2})$ single crystals, grown by tri-arc pulling technique were studied by echo-pulse ultrasonic probing. For the first time we have measured room temperature velocities of longitudinal and transverse sound waves. The measured diagonal elastic constants in the monoclinic phase are: $c_{33}=1.36\times10^{12},c_{44}=5.17\times10^{11},c_{55}=3.39\times10^{11}$dyne/cm$^{2}$. Here x and z are Cartesian axes parallel to crystallographic directions a and c; the later coincides with a two-fold rotation axis of the crystal.Work in Ames is supported by the US DOE.Work in NHMFL is supported by the In-House Research Program, NSF and State of Florida. [Preview Abstract] |
Tuesday, March 22, 2005 3:42PM - 3:54PM |
L28.00007: Phase locking transitions in arrays of coupled anharmonic oscillators Sachin Telang, Julian Sheats, Stephan Haas The Chaotic Dynamics of Coupled Oscillator arrays with cubic anharmonicity is studied. Our model includes damping terms and external time dependent forces. These Coupled oscillators are either phase-lock or behave chaotically or hyperchaotically, depending upon the magnitude of their inter-oscillator coupling strength and the frequency of the applied external force. The associated Lyapunov exponents are determined indicating the type of attractor, and phase diagrams are presented. [Preview Abstract] |
Tuesday, March 22, 2005 3:54PM - 4:06PM |
L28.00008: Optical Conductivity of Weakly Ferromagnetic Metals Dermot Coffey The frequency and temperature dependences of the contributions to $\sigma(\omega)$ from impurity and phonon scattering are calculated using an extension to the paramagnon model due to Hirsch$^1$. This model includes both an on-site repulsion and a nearest neighbor ferromagnetic coupling. The Debye model is used for the phonons. The dependences of these contributions on the parameters of the model are presented. \vskip 8pt \noindent $^1$ J. E. Hirsch, Phys. Rev. B {\bf 40}, 2354 and 9061 (1989). [Preview Abstract] |
Tuesday, March 22, 2005 4:06PM - 4:18PM |
L28.00009: Direct measurement of the electron-phonon relaxation rate in thin metal films Ilari Maasilta, Lasse Taskinen, Jenni Karvonen, Jani Kivioja We have used normal metal-insulator-superconductor (NIS) tunnel junctions for ultrasensitive thermometry at sub-Kelvin temperatures. With the help of these thermometers, we have developed an ac-technique to measure the electron-phonon (e-p) scattering rate directly, without any other material or geometry dependent parameters, based on overheating the electron gas. The technique is based on Joule heating the electrons in the frequency range DC-10 MHz, and measuring the electron temperature in DC. Because of the nonlinearity of the electron-phonon coupling with respect to temperature, even the DC response will be affected, when the heating frequency reaches the natural cut-off determined by the e-p scattering rate. Results on thin Cu films show a $T^{4}$ behavior for the scattering rate, in agreement with indirect measurement of similar samples and numerical modeling of the non-linear response.\footnote{L. J. Taskinen, J. M. Kivioja, J. T. Karvonen, and I. J. Maasilta, phys. stat. sol. (c) {\bf 1}, 2856 (2004). },\footnote{J. T. Karvonen, L. J. Taskinen, I. J. Maasilta, phys. stat. sol. (c) {\bf 1}, 2799 (2004).} [Preview Abstract] |
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L28.00010: Electronic polarization in quasilinear chains Michael Springborg, Bernard Kirtman, Yi Dong Starting with a finite $k$-mesh version of a well-known equation of Blount, we show how various definitions proposed for the polarization of a long chain are related. Expressions used for infinite periodic chains in the `modern theory of polarization' are thereby obtained along with a new single-particle formulation. Separate intracellular and intercellular contributions to the polarization are identified and in application to infinite chains, the traditional sawtooth definition is found to be missing the latter. For a finite open chain the dipole moment depends upon how the chain is terminated, but the intracellular and intercellular polarization do not. All these results are illustrated through calculations with a simple H\"uckel-like model. [Preview Abstract] |
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