2,433 research outputs found
Phonon spectral function for an interacting electron-phonon system
Using exact diagonalzation techniques, we study a model of interacting
electrons and phonons. The spectral width of the phonons is found to be reduced
as the Coulomb interaction U is increased. For a system with two modes per
site, we find a transfer of coupling strength from the upper to the lower mode.
This transfer is reduced as U is increased. These results give a qualitative
explanation of differences between Raman and photoemission estimates of the
electron-phonon coupling constants for A3C60 (A= K, Rb).Comment: 4 pages, RevTeX, 2 eps figur
Metal-insulator transitions: Influence of lattice structure, Jahn-Teller effect, and Hund's rule coupling
We study the influence of the lattice structure, the Jahn-Teller effect and
the Hund's rule coupling on a metal-insulator transition in AnC60 (A= K, Rb).
The difference in lattice structure favors A3C60 (fcc) being a metal and A4C60
(bct) being an insulator, and the coupling to Hg Jahn-Teller phonons favors
A4C60 being nonmagnetic. The coupling to Hg (Ag) phonons decreases (increases)
the value Uc of the Coulomb integral at which the metal-insulator transition
occurs. There is an important partial cancellation between the Jahn-Teller
effect and the Hund's rule coupling.Comment: 4 pages, RevTeX, 3 eps figure, additional material available at
http://www.mpi-stuttgart.mpg.de/docs/ANDERSEN/fullerene
Discrete Hubbard-Stratonovich transformations for systems with orbital degeneracy
A discrete Hubbard-Stratonovich transformation is presented for systems with
an orbital degeneracy and a Hubbard Coulomb interaction without multiplet
effects. An exact transformation is obtained by introducing an external field
which takes values. Alternative approximate transformations are
presented, where the field takes fewer values, for instance two values
corresponding to an Ising spin.Comment: 4 pages, revtex, 1 eps figure, additional material avalable at
http://librix.mpi-stuttgart.mpg.de/docs/ANDERSEN/fullerene
Electron-phonon interaction and antiferromagnetic correlations
We study effects of the Coulomb repulsion on the electron-phonon interaction
(EPI) in a model of cuprates at zero and finite doping. We find that
antiferromagnetic correlations strongly enhance EPI effects on the electron
Green's function with respect to the paramagnetic correlated system, but the
net effect of the Coulomb interaction is a moderate suppression of the EPI.
Doping leads to additional suppression, due to reduced antiferromagnetic
correlations. In contrast, the Coulomb interaction strongly suppresses EPI
effects on phonons, but the suppression weakens with doping.Comment: 4 pages and 5 figure
Electron self-energy in A3C60 (A=K, Rb): Effects of t1u plasmon in GW approximation
The electron self-energy of the t1u states in A3C60 (A=K, Rb) is calculated
using the so-called GW approximation. The calculation is performed within a
model which considers the t1u charge carrier plasmon at 0.5 eV and takes into
account scattering of the electrons within the t1u band. A moderate reduction
(35 %) of the t1u band width is obtained.Comment: 4 pages, revtex, 1 figure more information at
http://www.mpi-stuttgart.mpg.de/dokumente/andersen/fullerene
Two Component Heat Diffusion Observed in CMR Manganites
We investigate the low-temperature electron, lattice, and spin dynamics of
LaMnO_3 (LMO) and La_0.7Ca_0.3MnO_3 (LCMO) by resonant pump-probe reflectance
spectroscopy. Probing the high-spin d-d transition as a function of time delay
and probe energy, we compare the responses of the Mott insulator and the
double-exchange metal to the photoexcitation. Attempts have previously been
made to describe the sub-picosecond dynamics of CMR manganites in terms of a
phenomenological three temperature model describing the energy transfer between
the electron, lattice and spin subsystems followed by a comparatively slow
exponential decay back to the ground state. However, conflicting results have
been reported. Here we first show clear evidence of an additional component in
the long term relaxation due to film-to-substrate heat diffusion and then
develop a modified three temperature model that gives a consistent account for
this feature. We confirm our interpretation by using it to deduce the bandgap
in LMO. In addition we also model the non-thermal sub-picosecond dynamics,
giving a full account of all observed transient features both in the insulating
LMO and the metallic LCMO.Comment: 6 pages, 5 figures http://link.aps.org/doi/10.1103/PhysRevB.81.064434
v2: Abstract correcte
Enhancing Tc in field-doped Fullerenes by applying uniaxial stress
Capitalizing on the two-dimensional nature of superconductivity in
field-effect doped C60, we show that it should be possible to increase the
transition temperature Tc by applying uniaxial stress perpendicular to the gate
electrode. This method not only holds the promise of substantially enhancing Tc
(by about 30 K per GPa), but also provides a sensitive check of the current
understanding of superconductivity in the doped Fullerenes.Comment: 3 pages RevTe
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