89 Matching Results

Search Results

Advanced search parameters have been applied.

in subjects: "Electron-Phonon Coupling"

open access

Rigid muffin-tin approximation for the electron-phonon interaction in transition metals

Progress in calculating the electron-phonon parameters of transition metals has been based on either the rigid muffin-tin approximation (RMTA) or the fitted modified tight-binding approximation (FMTBA). The RMTA has been shown to be remarkably accurate for average electron-phonon properties, but there are indications that RMTA matrix elements may be too small at low momentum transfer. An attempt is made to demonstrate these assertions concerning the accuracy of RMTA and the numerous electron-ph… more

Date: January 1, 1980

Creator: Butler, W. H.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

The influence of anharmonic phonons on the isotope effect in high- Tc oxides

Anharmonic phonons are examined to study the unusual isotope effect exponents for the high-{Tc} oxides. Within a simple model of anharmonicity, the mass dependences of the electron-phonon coupling constant {lambda} and the phonon frequency determine the isotope effect exponent {alpha} as a function of coupling strength. A model in which the outer wells of a multiple-well potential deepen as the orthorhombic/low temperature tetragonal phase transition in La{sub 2-x}M{sub x}CuO{sub 4} is approach… more

Date: January 1, 1992

Creator: Crespi, V.H. & Cohen, M.L.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Phonon effect on the temperature dependence of spin susceptibility and magnetization in metals

In many transition metals the paramagnetic spin susceptibility X increases with increasing temperature much beyond ordinary theories could account for. We demonstrate how the effect of the electron-phonon interactions enable us to understand such temperature dependence of X.

Date: June 1, 1985

Creator: Kim, D. J.; Tanaka, C. & Ukon, S.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Transition temperature of isotropic superconductors

Using the self-consistent solutions of the Eliashberg theory, the limitations on the superconducting critical temperature T/sub c/ of isotropic superconductors are discussed.

Date: April 1, 1976

Creator: Poon, S.J.

Item Type: Report

Partner: UNT Libraries Government Documents Department

open access

Optical pumping of hot phonons in GaAs

Optical pumping of hot LO phonons in GaAs has been studied as a function of the excitation photon frequency. The experimental results are in good agreement with a model calculation which includes both inter- and intra-valley electron-phonon scatterings. The GAMMA-L and GAMMA-X intervalley electron-phonon interactions in GaAs have been estimated.

Date: June 30, 1982

Creator: Collins, C.L. & Yu, P.Y.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Intra-stark relaxation of Nd sup 3+ in silicate glass: Subpicosecond accumulated photon echo experiments

We have directly measured in the time domain the rates of phonon-induced population relaxation within the {sup 4}G{sub 5/2}, {sup 2}G{sub 7/2} Stark manifold of Nd{sup 3+} in a silicate glass. At 13 K, these processes occur in the picosecond to subpicosecond time regime. The populations relaxation time increases with excitation frequency within each inhomogeneously broadened Stark component. Finally, the location of the Stark components within the entire inhomogeneous profile can be inferred fr… more

Date: January 1, 1989

Creator: Lee, H. W. H.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Statics and adiabatic dynamics of nonlinear excitations in defected polyacetylene

Within the Su, Schrieffer and Heeger model we have calculated, both analytically and numerically, the effects of model impurities on the electronic structure and lattice distortion of trans-polyacetylene. We find that the electron-phonon coupling may result in a fundamental alteration of the impurity level location. In simulated photoexcitation experiments on the defected system we find that, in addition to the kinks and breathers produced in the undefected system, ''trapped kinks'', excitons a… more

Date: January 1, 1985

Creator: Phillpot, S. R.; Baeriswyl, D.; Bishop, A. R. & Lomdahl, P. S.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Neutron scattering study at high pressure of the phonon softening in lead

The shift in the traverse phonon modes propagating along (zeta,0,0) and (zeta,zeta,zeta) in Pb have been measured up to pressures of 1.75 GPa (..delta..a/a/sub 0/ approx. equal to -0.0125), and little change in the softening of the (zeta,0,0,) mode was observed. As the superconducting transition temperature and the electron-phonon coupling decrease substantially in this range, the relation of phonon softening to lambda in Pb-Tl alloys is questioned.

Date: January 1, 1977

Creator: McWhan, D.B.; Dynes, R.C. & Shapiro, S.M.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Generation of nonequilibrium optical phonons in GaAs/AlAs quantum wells by intrasubband and intersubband scatterings

The generation of a nonequilibrium population of optical phonons by photoexcited hot electrons in semiconductor quantum wells is investigated theoretically. The microscopic model of electron-phonon interaction proposed by Huang and Zhu has been used to compute the distributions of confined longitudinal optical phonons and interface modes in GaAs/AlAs quantum wells as a function of well width. Experimental tests of the calculated distributions by Raman scattering are discussed.

Date: November 1, 1991

Creator: Wald, K.R.; Kim, Dai-sik & Yu, P.Y.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Coulomb correlations and optical gap in polyacetylene

A model including both electron-phonon coupling (as in the SSH Hamiltonian) and electron-electron interactions (on-site term U, nearest-neighbor term V) is treated within the variational scheme of Gutswiller. It is shown that for weak electron-phonon coupling the primary effect is a bond-order wave induced by electronic correlation, whereas the lattice dimerization is a secondary effect. Correspondingly the optical gap is mainly due to electronic correlation.

Date: January 1, 1986

Creator: Baeriswyl, D. & Maki, K.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

FY05 LDRD Final Report Mapping Phonons at High-pressure

In order to shed light on the intriguing, and not yet fully understood fcc-isostructural {gamma} {yields} {alpha} transition in cerium, we have begun an experimental program aimed at the determination of the pressure evolution of the transverse acoustic (TA) and longitudinal acoustic (LA) phonon dispersions up to and above the transition. {gamma}-Ce Crystals of 60-80 mm diameter and 20 mm thickness were prepared from a large ingot, obtained from Ames Lab, using laser cutting, micro-mechanical a… more

Date: February 10, 2006

Creator: Farber, D. L.; Antonangelli, D.; Beraud, A.; Krisch, M. & Aracne, C.

Item Type: Report

Partner: UNT Libraries Government Documents Department

open access

Calculations of resistivity and superconducting T/sub c/ in transition metals

A survey is given of various electron-phonon effects which have been calculated for the metals Nb, Mo, Ta, Pd, and Cu. These effects include the mass enhancement lambda, superconducting T/sub c/, electrical and thermal resistivity, Hall coefficient, magnetoresistance, and the successfully tested predictions of linewidths ..gamma../sub 0/ of phonons. The calculations use local density approximations (LDA) energy bands, experimental phonons, and the rigid muffin tin (RMT) approximation. Mesh size… more

Date: January 1, 1985

Creator: Allen, P. B.; Beaulac, T. P.; Khan, F. S.; Butler, W. H.; Pinski, F. J. & Swihart, J. C.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Diffraction theory of phonon scattered electrons

No Description Available.

Date: January 1, 1991

Creator: Wang, Z. L.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Interactions of energetic particles and clusters with solids

Ion beams are being applied for surface modifications of materials in a variety of different ways: ion implantation, ion beam mixing, sputtering, and particle or cluster beam-assisted deposition. Fundamental to all of these processes is the deposition of a large amount of energy, generally some keV's, in a localized area. This can lead to the production of defects, atomic mixing, disordering and in some cases, amorphization. Recent results of molecular dynamics computer simulations of energetic… more

Date: December 1, 1990

Creator: Averback, R.S.; Hsieh, Horngming (Illinois Univ., Urbana, IL (USA). Dept. of Materials Science and Engineering); Diaz de la Rubia, T. (Lawrence Livermore National Lab., CA (USA)) & Benedek, R. (Argonne National Lab., IL (USA))

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Quantum Monte Carlo simulations of the one-dimensional extended Hubbard model

We report preliminary results of an investigation of the thermodynamic properties of the extended Hubbard model in one- dimension, calculated with the world-line Monte Carlo method described by Hirsch et al. With strictly continuous world-lines, we are able to measure the expectation of operators that conserve fermion number locally, such as the energy and (spatial) occupation number. By permitting the world-lines to be broken'' stochastically, we may also measure the expectation of operators t… more

Date: January 1, 1989

Creator: Somsky, W.R. & Gubernatis, J.E.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

General many-body systems

The problem of how to visualize and sometimes solve a general many-body system is considered. The ideas are established in the context of very simple small systems, a Hubbard model and a coupled electron-phonon model, both on two lattice sites. These models are also solved to good approximation in the thermodynamic limit, although the Hubbard model is restricted to a small number of holes away from the Mott insulating state. Response functions are also considered. A fairly general many-body Ham… more

Date: January 1, 1989

Creator: Trugman, S. A.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Transport in small and/or random systems

This report discusses: transport in small systems; electron-phonon interactions in quantum wells; noise in small systems; laser propagation in the atmosphere; laser-aerosol interactions; transport properties of carriers in semiconductor quantum wells; light transmission in a particulate medium; and laser generation of shock waves in droplets. (LSP)

Date: May 14, 1987

Creator: Lax, M.

Item Type: Report

Partner: UNT Libraries Government Documents Department

open access

Progress in calculations of the superconducting properties of transition metals

First principles calculations of the electron--phonon parameters of d-band metals can now be performed to an accuracy of about 10% for averaged quantities such as the mass enhancement or the room temperature resistivity. Quantities such as the spectral function ..cap alpha../sup 2/F(..omega..) or the phonon linewidth which describe the electron--phonon interaction in more detail can also be calculated. Agreement between calculated and experimental phonon linewidths is generally good but there a… more

Date: January 1, 1979

Creator: Butler, W. H.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

The effect of strong Coulomb correlations on electron-phonon interactions in the copper oxides: Implications for transport

The effects of strong Coulomb correlations on the electron-phonon interactions in the high temperature superconductors are investigated. Very strong Coulomb correlations, which are essential for creating the insulating state at half filling, lead to a suppression of charge fluctuations as the insulator is approached. This thereby significantly reduces the electron-phonon coupling. We present a self-consistent frozen phonon'' scheme which is based on a Coulomb renormalized band structure of the … more

Date: January 1, 1990

Creator: Kim, J.H. (Johns Hopkins Univ., Baltimore, MD (USA). Dept. of Physics and Astronomy); Levin, K. (Chicago Univ., IL (USA). James Franck Inst.); Wentzcovitch, R. (Brookhaven National Lab., Upton, NY (USA)) & Auerbach, A. (Boston Univ., MA (USA). Dept. of Physics)

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Competing electron-electron/electron-phonon interactions and polyacetylene

Using Lanczos exact diagonalization, we investigate the effects of the competition between the electro-electron and electron-phonon interactions in the context of the 1-D tight-binding Peierls-Hubbard Hamiltonian, studying various structural, optical, and vibrational properties of strongly correlated systems. We use polyacetylene as our experimental guide, and perform a parameter space search to determine the level at which a unique set of parameters can model this prototypical conducting polym… more

Date: April 8, 1991

Creator: Gammel, J.T. (Los Alamos National Lab., NM (USA) Bayreuth Univ. (Germany, F.R.). Physics Inst.); Campbell, D.K. (Los Alamos National Lab., NM (USA)) & Loh, E.Y. Jr. (Thinking Machines Corp., Cambridge, MA (USA))

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Specific heat of La sub 2-x Sr sub x CuO sub 4 : Volume fraction of superconductivity; possible structural transition at 45K

Specific heat measurements on La{sub 1.85}Sr{sub 0.15}CuO{sub 4} show a linear correlation of the zero-field low-temperature linear term with the discontinuity at {Tc}, each of which provides a measure of the superconducting volume fraction. The correlation leads to an estimate of the normal-state density of electronic states which, together with the band structure calculated value, gives an electron-phonon interaction parameter that is too small to account for the superconductivity. For a samp… more

Date: March 1, 1990

Creator: Amato, A.; Fisher, R. A.; Phillips, N. E. (Lawrence Berkeley Lab., CA (USA)) & Torrance, J. B. (IBM Research Div., San Jose, CA (USA). Almaden Research Center)

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Far-infrared studies of superconducting V/sub 3/Si, Nb/sub 3/Ge, and Nb

Optical techniques in the far infrared region (10 to 200 cm/sup -1/) are to explore the basic superconducting behavior of the high temperature superconductors V/sub 3/Si, Nb/sub 3/Ge, Nb, and granular NbN. Such spectroscopy yields accurate gap values, information about the temperature dependence of superconducting properties, values of the electron-phonon spectral function, and insight into grain-to-grain coupling in inhomogeneous geometries. These results are used to calculate basic supercondu… more

Date: February 23, 1981

Creator: Perkowitz, S.

Item Type: Report

Partner: UNT Libraries Government Documents Department

open access

Theory of electron--photon scattering effects in metals. Progress report, December 1, 1976--November 30, 1977

The general areas in which the investigations were carried out are transport properties and quasiparticle lifetimes in normal metals and superconductors. The more specific research projects upon which progress is reported are (a) the calculation of order parameter relaxation times in aluminum, (b) transport coefficients of the noble metals (emphasizing deviations from Matthiessen's rule), (c) variational transport calculations for a superconductor, (d) some general results on quasiparticle rela… more

Date: January 1, 1977

Creator: Lawrence, W.E.

Item Type: Report

Partner: UNT Libraries Government Documents Department

open access

Theory of normal and superconducting properties of fullerene-based solids

Recent experiments on the normal-state and superconducting properties of fullerene-based solids are used to constrain the proposal theories of the electronic nature of these materials. In general, models of superconductivity based on electron pairing induced by phonons are consistent with electronic band theory. The latter experiments also yield estimates of the parameters characterizing these type H superconductors. It is argued that, at this point, a standard model'' of phonons interacting wi… more

Date: October 1, 1992

Creator: Cohen, M.L.

Item Type: Report

Partner: UNT Libraries Government Documents Department