558 research outputs found
Anderson transitions in three-dimensional disordered systems with randomly varying magnetic flux
The Anderson transition in three dimensions in a randomly varying magnetic
flux is investigated in detail by means of the transfer matrix method with high
accuracy. Both, systems with and without an additional random scalar potential
are considered. We find a critical exponent of with random
scalar potential. Without it, is smaller but increases with the system
size and extrapolates within the error bars to a value close to the above. The
present results support the conventional classification of universality classes
due to symmetry.Comment: 4 pages, 2 figures, to appear in Phys. Rev.
Nonchiral Edge States at the Chiral Metal Insulator Transition in Disordered Quantum Hall Wires
The quantum phase diagram of disordered wires in a strong magnetic field is
studied as a function of wire width and energy. The two-terminal conductance
shows zero-temperature discontinuous transitions between exactly integer
plateau values and zero. In the vicinity of this transition, the chiral
metal-insulator transition (CMIT), states are identified that are
superpositions of edge states with opposite chirality. The bulk contribution of
such states is found to decrease with increasing wire width. Based on exact
diagonalization results for the eigenstates and their participation ratios, we
conclude that these states are characteristic for the CMIT, have the appearance
of nonchiral edges states, and are thereby distinguishable from other states in
the quantum Hall wire, namely, extended edge states, two-dimensionally (2D)
localized, quasi-1D localized, and 2D critical states.Comment: replaced with revised versio
Signatures of electron correlations in the transport properties of quantum dots
The transition matrix elements between the correlated and
electron states of a quantum dot are calculated by numerical diagonalization.
They are the central ingredient for the linear and non--linear transport
properties which we compute using a rate equation. The experimentally observed
variations in the heights of the linear conductance peaks can be explained. The
knowledge of the matrix elements as well as the stationary populations of the
states allows to assign the features observed in the non--linear transport
spectroscopy to certain transition and contains valuable information about the
correlated electron states.Comment: 4 pages (revtex,27kB) + 3 figures in one file ziped and uuencoded
(postscript,33kB), to appear in Phys.Rev.B as Rapid Communicatio
Tunneling between two Luttinger liquids with long range interaction
The non linear charge transfer through a tunnel junction between two
Luttinger systems is studied for repulsive, finite range interaction between
electrons on the same, V_{11}, and on different,V_{12}, sides of the junction.
Features of the Coulomb blockade effect are observed if V_{12}=0. We predict a
novel interaction induced enhancement of the current if V_{12}>0. When
V_{12}=V_{11}, the current is suppressed at small bias, but the ``charging
energy'', obtained from the asymptotic behavior at high bias voltage, vanishes.Comment: 4 pages, RevTeX, to be published in Physical Review B (Brief Report
Phase diagram of localization in a magnetic field
The phase diagram of localization is numerically calculated for a
three-dimensional disordered system in the presence of a magnetic field using
the Peierls substitution. The mobility edge trajectory shifts in the
energy-disorder space when increasing the field. In the band center, localized
states near the phase boundary become delocalized. The obtained field
dependence of the critical disorder is in agreement with a power law behavior
expected from scaling theory. Close to the tail of the band the magnetic field
causes localization of extended states.Comment: 4 pages, RevTeX, 3 PS-figures (4 extra references are included, minor
additions), to appear in Phys. Rev. B as a Brief Repor
Asymptotics of Universal Probability of Neighboring Level Spacings at the Anderson Transition
The nearest-neighbor level spacing distribution is numerically investigated
by directly diagonalizing disordered Anderson Hamiltonians for systems of sizes
up to 100 x 100 x 100 lattice sites. The scaling behavior of the level
statistics is examined for large spacings near the delocalization-localization
transition and the correlation length exponent is found. By using
high-precision calculations we conjecture a new interpolation of the critical
cumulative probability, which has size-independent asymptotic form \ln I(s)
\propto -s^{\alpha} with \alpha = 1.0 \pm 0.1.Comment: 5 pages, RevTex, 4 figures, to appear in Physical Review Letter
Time-dependent Ginzburg-Landau equations for mixed d- and s-wave superconductors
A set of coupled time-dependent Ginzburg-Landau equations (TDGL) for
superconductors of mixed d- and s-wave symmetry are derived microscopically
from the Gor'kov equations by using the analytical continuation technique. The
scattering effects due to impurities with both nonmagnetic and magnetic
interactions are considered. We find that the d- and s-wave components of the
order parameter can have very different relaxation times in the presence of
nonmagnetic impurities. This result is contrary to a set of phenomenologically
proposed TDGL equations and thus may lead to new physics in the dynamics of
flux motion.Comment: 22 pages, 6 figures are available upon request, to appear in Phys.
Rev.
Coherent Potential Approximation for `d - wave' Superconductivity in Disordered Systems
A Coherent Potential Approximation is developed for s-wave and d-wave
superconductivity in disordered systems. We show that the CPA formalism
reproduces the standard pair-breaking formula, the self-consistent Born
Approximation and the self-consistent T-matrix approximation in the appropriate
limits. We implement the theory and compute T_c for s-wave and d-wave pairing
using an attractive nearest neighbor Hubbard model featuring both binary alloy
disorder and a uniform distribution of scattering site potentials. We determine
the density of states and examine its consequences for low temperature heat
capacity. We find that our results are in qualitative agreement with
measurements on Zn doped YBCO superconductors.Comment: 35 pages, 23 figures, submitted to Phys Rev.
Smoothed universal correlations in the two-dimensional Anderson model
We report on calculations of smoothed spectral correlations in the
two-dimensional Anderson model for weak disorder. As pointed out in (M.
Wilkinson, J. Phys. A: Math. Gen. 21, 1173 (1988)), an analysis of the
smoothing dependence of the correlation functions provides a sensitive means of
establishing consistency with random matrix theory. We use a semiclassical
approach to describe these fluctuations and offer a detailed comparison between
numerical and analytical calculations for an exhaustive set of two-point
correlation functions. We consider parametric correlation functions with an
external Aharonov-Bohm flux as a parameter and discuss two cases, namely broken
time-reversal invariance and partial breaking of time-reversal invariance.
Three types of correlation functions are considered: density-of-states,
velocity and matrix element correlation functions. For the values of smoothing
parameter close to the mean level spacing the semiclassical expressions and the
numerical results agree quite well in the whole range of the magnetic flux.Comment: 12 pages, 14 figures submitted to Phys. Rev.
Behavior of the thermopower in amorphous materials at the metal-insulator transition
Published versio
- …