205 research outputs found
Screened Interaction and Self-Energy in an Infinitesimally Polarized Electron Gas via the Kukkonen-Overhauser Method
The screened electron-electron interaction and the
electron self-energy in an infinitesimally polarized electron gas are derived
by extending the approach of Kukkonen and Overhauser. Various quantities in the
expression for are identified in terms of the relevant
response functions of the electron gas. The self-energy is obtained from
by making use of the GW method which in this case
represents a consistent approximation. Contact with previous calculations is
made.Comment: 7 page
Orbital ordering in undoped manganites via a generalized Peierls instability
We study the ground state orbital ordering of , at weak
electron-phonon coupling, when the spin state is A-type antiferromagnet. We
determine the orbital ordering by extending to our Jahn-Teller system a
recently developed Peierls instability framework for the Holstein model [1]. By
using two-dimensional dynamic response functions corresponding to a mixed
Jahn-Teller mode, we establish that the mode determines the orbital
order.Comment: A few changes made. Accepted in Phys. Rev.
Charge and Spin Response of the Spin--Polarized Electron Gas
The charge and spin response of a spin--polarized electron gas is
investigated including terms beyond the random phase approximation. We evaluate
the charge response, the longitudinal and transverse spin response, and the
mixed spin--charge response self--consistently in terms of the susceptibility
functions of a non--interacting system. Exchange--correlation effects between
electrons of spin and are included following Kukkonen and
Overhauser, by using spin--polarization dependent generalized Hubbard local
field factors and . The general
condition for charge--density and spin--density--wave excitations of the system
is discussed.Comment: 4 pages, latex, no figure
Peierls to superfluid crossover in the one-dimensional, quarter-filled Holstein model
We use continuous-time quantum Monte Carlo simulations to study retardation
effects in the metallic, quarter-filled Holstein model in one dimension. Based
on results which include the one- and two-particle spectral functions as well
as the optical conductivity, we conclude that with increasing phonon frequency
the ground state evolves from one with dominant diagonal order---2k_F charge
correlations---to one with dominant off-diagonal fluctuations, namely s-wave
pairing correlations. In the parameter range of this crossover, our numerical
results support the existence of a spin gap for all phonon frequencies. The
crossover can hence be interpreted in terms of preformed pairs corresponding to
bipolarons, which are essentially localised in the Peierls phase, and
"condense" with increasing phonon frequency to generate dominant pairing
correlations.Comment: 11 pages, 5 figure
Jahn-Teller polarons and their superconductivity in a molecular conductor
We present a theoretical study of a possibility of superconductivity in a
three dimensional molecular conductor in which the interaction between
electrons in doubly degenerate molecular orbitals and an {\em intra}molecular
vibration mode is large enough to lead to the formation of
Jahn-Teller small polarons. We argue that the effective polaron-polaron
interaction can be attractive for material parameters realizable in molecular
conductors. This interaction is the source of superconductivity in our model.
On analyzing superconducting instability in the weak and strong coupling
regimes of this attractive interaction, we find that superconducting transition
temperatures up to 100 K are achievable in molecular conductors within this
mechanism. We also find, for two particles per molecular site, a novel Mott
insulating state in which a polaron singlet occupies one of the doubly
degenerate orbitals on each site. Relevance of this study in the search for new
molecular superconductors is pointed out.Comment: Submitted to Phys. Rev.
Interaction-Induced Enhancement of Spin-Orbit Coupling in Two-Dimensional Electronic System
We study theoretically the renormalization of the spin-orbit coupling
constant of two-dimensional electrons by electron-electron interactions. We
demonstrate that, similarly to the factor, the renormalization corresponds
to the enhancement, although the magnitude of the enhancement is weaker than
that for the factor. For high electron concentrations (small interaction
parameter ) the enhancement factor is evaluated analytically within the
static random phase approximation. For large we use an approximate
expression for effective electron-electron interaction, which takes into
account the local field factor, and calculate the enhancement numerically. We
also study the interplay between the interaction-enhanced Zeeman splitting and
interaction-enhanced spin-orbit coupling.Comment: 18 pages, 2 figures, REVTe
Observation of spin Coulomb drag in a two-dimensional electron gas
An electron propagating through a solid carries spin angular momentum in
addition to its mass and charge. Of late there has been considerable interest
in developing electronic devices based on the transport of spin, which offer
potential advantages in dissipation, size, and speed over charge-based devices.
However, these advantages bring with them additional complexity. Because each
electron carries a single, fixed value (-e) of charge, the electrical current
carried by a gas of electrons is simply proportional to its total momentum. A
fundamental consequence is that the charge current is not affected by
interactions that conserve total momentum, notably collisions among the
electrons themselves. In contrast, the electron's spin along a given spatial
direction can take on two values, "up" and "down", so that the spin current and
momentum need not be proportional. Although the transport of spin polarization
is not protected by momentum conservation, it has been widely assumed that,
like the charge current, spin current is unaffected by electron-electron (e-e)
interactions. Here we demonstrate experimentally not only that this assumption
is invalid, but that over a broad range of temperature and electron density,
the flow of spin polarization in a two-dimensional gas of electrons is
controlled by the rate of e-e collisions
Correlation energy and spin polarization in the 2D electron gas
The ground state energy of the two--dimensional uniform electron gas has been
calculated with fixed--node diffusion Monte Carlo, including backflow
correlations, for a wide range of electron densities as a function of spin
polarization. We give a simple analytic representation of the correlation
energy which fits the density and polarization dependence of the simulation
data and includes several known high- and low-density limits. This
parametrization provides a reliable local spin density energy functional for
two-dimensional systems and an estimate for the spin susceptibility. Within the
proposed model for the correlation energy, a weakly first--order polarization
transition occurs shortly before Wigner crystallization as the density is
lowered.Comment: Minor typos corrected, see erratum: Phys. Rev. Lett. 91, 109902(E)
(2003
Electron-electron interactions and two-dimensional - two-dimensional tunneling
We derive and evaluate expressions for the dc tunneling conductance between
interacting two-dimensional electron systems at non-zero temperature. The
possibility of using the dependence of the tunneling conductance on voltage and
temperature to determine the temperature-dependent electron-electron scattering
rate at the Fermi energy is discussed. The finite electronic lifetime produced
by electron-electron interactions is calculated as a function of temperature
for quasiparticles near the Fermi circle. Vertex corrections to the random
phase approximation substantially increase the electronic scattering rate. Our
results are in an excellent quantitative agreement with experiment.Comment: Revtex style, 21 pages and 8 postscript figures in a separate file;
Phys. Rev. B (in press
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