38 research outputs found
Density Waves in a Transverse Electric Field
In a quasi-one-dimensional conductor with an open Fermi surface, a Charge or
a Spin Density Wave phase can be destroyed by an electric field perpendicular
to the direction of high conductivity. This mechanism, due to the breakdown of
electron-hole symmetry, is very similar to the orbital destruction of
superconductivity by a magnetic field, due to time-reversal symmetry.Comment: 3 pages, Latex, 2 figures, to appear in Phys. Rev. B Rapid Com
Fermi Liquid Theory and Ferromagnetic Manganites at Low Temperatures
Fermi liquid characteristics for ferromagnetic ~manganites,
ABMnO, are evaluated in the tight-binding approximation and
compared with experimental data for the best studied region . The
bandwidths change only slightly for different compositions. The Sommerfeld
coefficient, , the -term in resistivity and main scales in optical
conductivity agree well with the two band model. The ``2.5'' - transition due
to a ``neck'' forming at Fermi surface, is found at . The mean free path
may change from 3 to 80 interatomic distances in the materials, indicating that
samples' quality remains a pressing issue for the better understanding of
manganites.Comment: 4 pages, 2 figures. Submitted to Solid State Com
Transport Properties of "Extended-s" State Superconductors
Superconducting states with "extended s-wave" symmetry have been suggested in
connection with recent ARPES experiments on BSCCO. In the presence of
impurities, thermodynamic properties of such states reflect a residual density
of states for a range of concentrations. While properties reflecting
alone will be similar to those of d-wave states, transport
measurements may be shown to qualitatively distinguish between the two. In
contrast to the d-wave case with unitarity limit scattering, limiting
low-temperature residual conductivities in the s-wave state are large and scale
inversely with impurity concentration.Comment: 4 pages, 5 figures, uuencoded compressed postscript fil
Dynamics of 2D pancake vortices in layered superconductors
The dynamics of 2D pancake vortices in Josephson-coupled
superconducting/normal - metal multilayers is considered within the
time-dependent Ginzburg-Landau theory. For temperatures close to a
viscous drag force acting on a moving 2D vortex is shown to depend strongly on
the conductivity of normal metal layers. For a tilted vortex line consisting of
2D vortices the equation of viscous motion in the presence of a transport
current parallel to the layers is obtained. The specific structure of the
vortex line core leads to a new dynamic behavior and to substantial deviations
from the Bardeen-Stephen theory. The viscosity coefficient is found to depend
essentially on the angle between the magnetic field and the
axis normal to the layers. For field orientations close to the layers
the nonlinear effects in the vortex motion appear even for slowly moving vortex
lines (when the in-plane transport current is much smaller than the
Ginzburg-Landau critical current). In this nonlinear regime the viscosity
coefficient depends logarithmically on the vortex velocity .Comment: 15 pages, revtex, no figure
Evolution of wave packets in quasi-1D and 1D random media: diffusion versus localization
We study numerically the evolution of wavepackets in quasi one-dimensional
random systems described by a tight-binding Hamiltonian with long-range random
interactions. Results are presented for the scaling properties of the width of
packets in three time regimes: ballistic, diffusive and localized. Particular
attention is given to the fluctuations of packet widths in both the diffusive
and localized regime. Scaling properties of the steady-state distribution are
also analyzed and compared with theoretical expression borrowed from
one-dimensional Anderson theory. Analogies and differences with the kicked
rotator model and the one-dimensional localization are discussed.Comment: 32 pages, LaTex, 11 PostScript figure
Toward a Unified Magnetic Phase Diagram of the Cuprate Superconductors
We propose a unified magnetic phase diagram of cuprate superconductors. A new
feature of this phase diagram is a broad intermediate doping region of
quantum-critical, , behavior, characterized by temperature independent
and linear , where the spin waves are not completely
absorbed by the electron-hole continuum. The spin gap in the moderately doped
materials is related to the suppression of the low-energy spectral weight in
the quantum disordered, , regime. The crossover to the regime, where
T_1T/T_{\rm 2G}^2 \simeq \mbox{const}, occurs only in the fully doped
materials.Comment: 14 pages, REVTeX v2.1, PostScript file for 3 figures attached,
UIUC-P-93-06-04
Disorder Effects in Two-Dimensional d-wave Superconductors
Influence of weak nonmagnetic impurities on the single-particle density of
states of two-dimensional electron systems with a conical
spectrum is studied. We use a nonperturbative approach, based on replica trick
with subsequent mapping of the effective action onto a one-dimensional model of
interacting fermions, the latter being treated by Abelian and non-Abelian
bosonization methods. It is shown that, in a d-wave superconductor, the density
of states, averaged over randomness, follows a nontrivial power-law behavior
near the Fermi energy: . The exponent
is calculated for several types of disorder. We demonstrate that the
property is a direct consequence of a {\it continuous} symmetry
of the effective fermionic model, whose breakdown is forbidden in two
dimensions. As a counter example, we consider another model with a conical
spectrum - a two-dimensional orbital antiferromagnet, where static disorder
leads to a finite due to breakdown of a {\it discrete}
(particle-hole) symmetry.Comment: 24 pages, 3 figures upon request, RevTe
Onset of Vortices in Thin Superconducting Strips and Wires
Spontaneous nucleation and the consequent penetration of vortices into thin
superconducting films and wires, subjected to a magnetic field, can be
considered as a nonlinear stage of primary instability of the current-carrying
superconducting state. The development of the instability leads to the
formation of a chain of vortices in strips and helicoidal vortex lines in
wires. The boundary of instability was obtained analytically. The nonlinear
stage was investigated by simulations of the time-dependent generalized
Ginzburg-Landau equation.Comment: REVTeX 3.0, 12 pages, 5Postscript figures (uuencoded). Accepted for
Phys. Rev.
Quantum Hall Effect in Three-dimensional Field-Induced Spin Density Wave Phases with a Tilted Magnetic Field
The quantum Hall effect in the three-dimensional anisotropic tight-binding
electrons is investigated in the field-induced spin density wave phases with a
magnetic field tilted to any direction. The Hall conductivity,
and , are shown to be quantized as a function of the wave vector
of FISDW, while stays zero, where is the most conducting
direction and and are perpendicular to .Comment: 18 pages, REVTeX 3.0, 1 figure is available upon request, to be
published in Physical Review
Fractional vortices on grain boundaries --- the case for broken time reversal symmetry in high temperature superconductors
We discuss the problem of broken time reversal symmetry near grain boundaries
in a d-wave superconductor based on a Ginzburg-Landau theory. It is shown that
such a state can lead to fractional vortices on the grain boundary. Both
analytical and numerical results show the structure of this type of state.Comment: 9 pages, RevTeX, 5 postscript figures include