4 research outputs found
Magnetoresistance of p-GaAs/AlGaAs structures in the vicinity of metal-insulator transition: Effect of superconducting leads
Experimental and theoretical studies on transport in semiconductor samples
with superconducting electrodes are reported. We focus on the samples close to
metal-insulator transition. In metallic samples, a peak of negative
magnetoresistance at fields lower than critical magnetic field of the leads was
observed. This peak is attributed to restoration of a single-particle tunneling
emerging with suppression of superconductivity. The experimental results allow
us to estimate tunneling transparency of the boundary between superconductor
and metal. In contrast, for the insulating samples no such a peak was observed.
We explain this behavior as related to properties of transport through the
contact between superconductor and hopping conductor. This effect can be used
to discriminate between weak localization and strong localization regimes.Comment: 10 pages, 3 fi
Zero-bias anomaly in disordered wires
We calculate the low-energy tunneling density of states of
an -channel disordered wire, taking into account the electron-electron
interaction non-perturbatively. The finite scattering rate results in
a crossover from the Luttinger liquid behavior at higher energies,
, to the exponential dependence at low energies, where
. At finite temperature , the tunneling
density of states depends on the energy through the dimensionless variable
. At the Fermi level .Comment: 5 pages, 1 figur
Variational quantum Monte Carlo study of two-dimensional Wigner crystals: exchange, correlation, and magnetic field effects
The two-dimensional Wigner crystals are studied with the variational quantum
Monte Carlo method. The close relationship between the ground-state
wavefunction and the collective excitations in the system is illustrated, and
used to guide the construction of the ground-state wavefunction of the strongly
correlated solid. Exchange, correlation, and magnetic field effects all give
rise to distinct physical phenomena. In the absence of any external magnetic
field, interesting spin-orderings are observed in the ground-state of the
electron crystal in various two-dimensional lattices. In particular,
two-dimensional bipartite lattices are shown not to lead necessarily to an
antiferromagnetic ground-state. In the quantum Hall effect regime, a strong
magnetic field introduces new energy and length scales. The magnetic field
quenches the kinetic energy and poses constraints on how the electrons may
correlate with each other. Care is taken to ensure the appropriate
translational properties of the wavefunction when the system is in a uniform
magnetic field. We have examined the exchange, intra-Landau-level correlation
as well as Landau-level-mixing effects with various variational wavefunctions.
We also determine their dependences on the experimental parameters such as the
carrier effective mass at a modulation-doped semiconductor heterojunction. Our
results, when combined with some recent calculations for the energy of the
fractional quantum Hall liquid including Landau-level-mixing, show
quantitatively that in going from -doping to -doping in
heterojunction systems, the crossover filling factor from the fractional
quantum Hall liquid to the Wigner crystal changes from filling factor to . This lends strong support to the claim that theComment: LaTex file, 14 figures available from [email protected]