1,647 research outputs found
Monte Carlo simulation method for Laughlin-like states in a disk geometry
We discuss an alternative accurate Monte Carlo method to calculate the
ground-state energy and related quantities for Laughlin states of the
fractional quantum Hall effect in a disk geometry. This alternative approach
allows us to obtain accurate bulk regime (thermodynamic limit) values for
various quantities from Monte Carlo simulations with a small number of
particles (much smaller than that needed with standard Monte Carlo approaches).Comment: 13 pages, 6 figures, 2 table
Field-induced breakdown of the quantum Hall effect
A numerical analysis is made of the breakdown of the quantum Hall effect
caused by the Hall electric field in competition with disorder. It turns out
that in the regime of dense impurities, in particular, the number of localized
states decreases exponentially with the Hall field, with its dependence on the
magnetic and electric field summarized in a simple scaling law. The physical
picture underlying the scaling law is clarified. This intra-subband process,
the competition of the Hall field with disorder, leads to critical breakdown
fields of magnitude of a few hundred V/cm, consistent with observations, and
accounts for their magnetic-field dependence \propto B^{3/2} observed
experimentally. Some testable consequences of the scaling law are discussed.Comment: 7 pages, Revtex, 3 figures, to appear in Phys. Rev.
Thermodynamic Study of Excitations in a 3D Spin Liquid
In order to characterize thermal excitations in a frustrated spin liquid, we
have examined the magnetothermodynamics of a model geometrically frustrated
magnet. Our data demonstrate a crossover in the nature of the spin excitations
between the spin liquid phase and the high-temperature paramagnetic state. The
temperature dependence of both the specific heat and magnetization in the spin
liquid phase can be fit within a simple model which assumes that the spin
excitations have a gapped quadratic dispersion relation.Comment: 5 figure
Rational sequences for the conductance in quantum wires from affine Toda field theories
We analyse the expression for the conductance of a quantum wire which is
decribed by an integrable quantum field theory. In the high temperature regime
we derive a simple formula for the filling fraction. This expression involves
only the inverse of a matrix which contains the information of the asymptotic
phases of the scattering matrix and the solutions of the constant thermodynamic
Bethe ansatz equations. Evaluating these expressions for minimal affine Toda
field theory we recover several sequences of rational numbers, which are
multiples of the famous Jain sequence for the filling fraction occurring in the
context of the fractional quantum Hall effect. For instance we obtain for -minimal affine Toda field theory. The matrices
involved have in general non-rational entries and are not part of previous
classification schemes based on integral lattices.Comment: 9 pages Latex, version to appear in Journal of Physics
Strong, Ultra-narrow Peaks of Longitudinal and Hall Resistances in the Regime of Breakdown of the Quantum Hall Effect
With unusually slow and high-resolution sweeps of magnetic field, strong,
ultra-narrow (width down to ) resistance peaks are observed in
the regime of breakdown of the quantum Hall effect. The peaks are dependent on
the directions and even the history of magnetic field sweeps, indicating the
involvement of a very slow physical process. Such a process and the sharp peaks
are, however, not predicted by existing theories. We also find a clear
connection between the resistance peaks and nuclear spin polarization.Comment: 5 pages with 3 figures. To appear in PR
Josephson Plasma Resonance as a Structural Probe of Vortex Liquid
Recent developments of the Josephson plasma resonance and transport c-axis
measurements in layered high T superconductors allow to probe Josephson
coupling in a wide range of the vortex phase diagram. We derive a relation
between the field dependent Josephson coupling energy and the density
correlation function of the vortex liquid. This relation provides a unique
opportunity to extract the density correlation function of pancake vortices
from the dependence of the plasma resonance on the -component of the
magnetic field at a fixed -axis component.Comment: 4 pages, 1 fugure, accepted to Phys. Rev. Let
High Magnetic Field Microwave Conductivity of 2D Electrons in an Array of Antidots
We measure the high magnetic field () microwave conductivity,
Re, of a high mobility 2D electron system containing an antidot
array. Re vs frequency () increases strongly in the regime of
the fractional quantum Hall effect series, with Landau filling .
At microwave , Re vs exhibits a broad peak centered around
. On the peak, the 10 GHz Re can exceed its dc-limit
value by a factor of 5. This enhanced microwave conductivity is unobservable
for temperature K, and grows more pronounced as is
decreased. The effect may be due to excitations supported by the antidot edges,
but different from the well-known edge magnetoplasmons.Comment: 4 pages, 3 figures, revtex
Transverse optical plasmons in layered superconductors
We discuss the possible existance of transverse optical plasma modes in
superlattices consisting of Josephson coupled superconducting layers. These
modes appear as resonances in the current-current correlation function, as
opposed to the usual plasmons which are poles in the density-density channel.
We consider both bilayer superlattices, and single layer lattices with a spread
of interlayer Josephson couplings. We show that our model is in quantitative
agreement with the recent experimental observation by a number of groups of a
peak at the Josephson plasma frequency in the optical conductivity of
LaSrCuOComment: Proceedings of LT21, in press, 4 pages, Latex with LTpaper.sty and
epsfig.sty, 2 postscript figure
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