651 research outputs found
Dynamic ion structure factor of warm dense matter
The dynamics of the ion structure in warm dense matter is determined by molecular dynamics simulations using an effective ion-ion potential. This potential is obtained from ab initio simulations and has a strong short-range repulsion added to a screened Coulomb potential. Models based on static or dynamic local field corrections are found to be insufficient to describe the data. An extended Mermin approach, a hydrodynamic model, and the method of moments with local constraints are capable of reproducing the numerical results but have rather limited predictive powers as they all need some numerical data as input. The method of moments is found to be the most promising
Photoluminescence spectrum of an interacting two-dimensional electron gas at \nu=1
We report on the theoretical photoluminescence spectrum of the interacting
two-dimensional electron gas at filling factor one (\nu=1). We considered a
model similar to the one adopted to study the X-ray spectra of metals and
solved it analytically using the bosonization method previously developed for
the two-dimensional electron gas at \nu=1. We calculated the emission spectra
of the right and the left circularly polarized radiations for the situations
where the distance between the two-dimensional electron gas and the valence
band hole are smaller and greater than the magnetic length. For the former, we
showed that the polarized photoluminescence spectra can be understood as the
recombination of the so-called excitonic state with the valence band hole
whereas, for the latter, the observed emission spectra can be related to the
recombination of a state formed by a spin down electron bound to n spin waves.
This state seems to be a good description for the quantum Hall skyrmion.Comment: Revised version, 10 pages, 5 figures, accepted to Phys. Rev.
One-electron self energies and spectral functions for the t-J model in the large-N limit
Using a recently developed perturbative approach, which considers Hubbard
operators as fundamental excitations, we have performed electronic self-energy
and spectral function calculations for the model on the square lattice.
We have found that the spectral functions along the Fermi surface are
isotropic, even close to the critical doping where the -density wave phase
takes place. Fermi liquid behavior with scattering rate and a
finite quasiparticle weight was obtained. decreases with decreasing
doping taking low values for low doping. Results are compared with other ones,
analytical and numerical like slave-boson and Lanczos diagonalization finding
agreement. We discuss our results in the light of recent experiments in
cuprates.Comment: 10 pages, 9 figures, accepted for publication in Phys. Rev.
Artifact of the phonon-induced localization by variational calculations in the spin-boson model
We present energy and free energy analyses on all variational schemes used in
the spin-boson model at both T=0 and . It is found that all the
variational schemes have fail points, at where the variational schemes fail to
provide a lower energy (or a lower free energy at ) than the
displaced-oscillator ground state and therefore the variational ground state
becomes unstable, which results in a transition from a variational ground state
to a displaced oscillator ground state when the fail point is reached. Such
transitions are always misidentied as crossover from a delocalized to localized
phases in variational calculations, leading to an artifact of phonon-induced
localization. Physics origin of the fail points and explanations for different
transition behaviors with different spectral functions are found by studying
the fail points of the variational schemes in the single mode case.Comment: 9 pages, 7 figure
Role of electron-electron and electron-phonon interaction effect in the optical conductivity of VO2
We have investigated the charge dynamics of VO2 by optical reflectivity
measurements. Optical conductivity clearly shows a metal-insulator transition.
In the metallic phase, a broad Drude-like structure is observed. On the other
hand, in the insulating phase, a broad peak structure around 1.3 eV is
observed. It is found that this broad structure observed in the insulating
phase shows a temperature dependence. We attribute this to the electron-phonon
interaction as in the photoemission spectra.Comment: 6 pages, 8 figures, accepted for publication in Phys. Rev.
Zn-impurity effects on quasi-particle scattering in La2-xSrxCuO4 studied by angle-resolved photoemission spectroscopy
Angle-resolved photoemission measurements were performed on Zn-doped
La2-xSrxCuO4 (LSCO) to investigate the effects of Zn impurities on the low
energy electronic structure. The Zn-impurity-induced increase in the
quasi-particle (QP) width in momentum distribution curves (MDC) is
approximately isotropic on the entire Fermi surface and energy-independent near
the Fermi level (EF). The increase in the MDC width is consistent with the
increase in the residual resistivity due to the Zn impurities if we assume the
carrier number to be 1-x for x=0.17 and the Zn impurity to be a potential
scatterer close to the unitarity limit. For x=0.03, the residual resistivity is
found to be higher than that expected from the MDC width, and the effects of
antifferomagnetic fluctuations induced around the Zn impurities are discussed.
The leading edges of the spectra near (pi,0) for x=0.17 are shifted toward
higher energies relative to EF with Zn substitution, indicating a reduction of
the superconducting gap.Comment: 7 pages, 7 figure
Calculation of overdamped c-axis charge dynamics and the coupling to polar phonons in cuprate superconductors
In our recent paper we presented empirical evidences suggesting that
electrons in cuprate superconductors are strongly coupled to unscreened c-axis
polar phonons. In the overdoped regime the c-axis metallizes and we present
here simple theoretical arguments demonstrating that the observed effect of the
metallic c-axis screening on the polar electron-phonon coupling is consistent
with a strongly overdamped c-axis charge dynamics in the optimally doped
system, becoming less dissipative in the overdoped regime.Comment: 6 pages, 1 figure. to be published in Phys. Rev.
Determination of the electronic structure of bilayer graphene from infrared spectroscopy results
We present an experimental study of the infrared conductivity, transmission,
and reflection of a gated bilayer graphene and their theoretical analysis
within the Slonczewski-Weiss-McClure (SWMc) model. The infrared response is
shown to be governed by the interplay of the interband and the intraband
transitions among the four bands of the bilayer. The position of the main
conductivity peak at the charge neutrality point is determined by the
interlayer tunneling frequency. The shift of this peak as a function of the
gate voltage gives information about less known parameters of the SWMc model,
in particular, those responsible for the electron-hole and sublattice
asymmetries. These parameter values are shown to be consistent with recent
electronic structure calculations for the bilayer graphene and the SWMc
parameters commonly used for the bulk graphite.Comment: (v2) 11 pages, 7 figures; Important typo fixes and bibliography
addition
Small-q electron-phonon scattering and linear dc resistivity in high-T_c oxides
We examine the effect on the DC resistivity of small-q electron-phonon
scattering, in a system with the electronic topology of the high-T_c oxides.
Despite the fact that the scattering is dominantly forward, its contribution to
the transport can be significant due to ``ondulations'' of the bands in the
flat region and to the umpklapp process. When the extended van-Hove
singularities are sufficiently close to the acoustic branch of the
phonons contribute significantly to the transport. In that case one can obtain
linear dependent resistivity down to temperatures as low as 10 K, even if
electrons are scattered also by optical phonons of about 500 K as reported by
Raman measurements.Comment: LATEX file and 4 Postscript figure
Analytical Results for a Hole in an Antiferromagnet
The Green's function for a hole moving in an antiferromagnet is derived
analytically in the long-wavelength limit. We find that the infrared divergence
is eliminated in two and higher dimensions so that the quasiparticle weight is
finite. Our results also suggest that the hole motion is polaronic in nature
with a bandwidth proportional to ( is a constant).
The connection of the long-wavelength approximation to the first-order
approximation in the cumulant expansion is also clarified.Comment: 12 papes, 2 figures available upon request, revte
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