54 research outputs found
Collective charge density wave motion through an ensemble of Aharonov-Bohm rings
We investigate theoretically the collective charge density wave motion
through an ensemble of small disordered Aharonov-Bohm rings. It is shown that
the magnetic flux modulates the threshold field and the magnetoresistance with
a half flux quantum periodicity , resulting from ensemble
averaging over random scattering phases of multiple rings. The magnitude of the
magnetoresistance oscillations decreases rapidly with increasing bias. This is
consistent with recent experiments on in presence of columnar defects
[Phys. Rev. Lett. 78, 919 (1997)].Comment: 4 pages Revtex, 2 figures. Submitted to Phys. Rev. Let
Conductance length autocorrelation in quasi one-dimensional disordered wires
Employing techniques recently developed in the context of the Fokker--Planck
approach to electron transport in disordered systems we calculate the
conductance length correlation function
for quasi 1d wires. Our result is valid for arbitrary lengths L and .
In the metallic limit the correlation function is given by a squared
Lorentzian. In the localized regime it decays exponentially in both L and
. The correlation length is proportional to L in the metallic regime
and saturates at a value approximately given by the localization length
as .Comment: 23 pages, Revtex, two figure
Origin of Magic Angular Momentum in a Quantum Dot under Strong Magnetic Field
This paper investigates origin of the extra stability associated with
particular values (magic numbers) of the total angular momentum of electrons in
a quantum dot under strong magnetic field. The ground-state energy,
distribution functions of density and angular momentum, and pair correlation
function are calculated in the strong field limit by numerical diagonalization
of the system containing up to seven electrons. It is shown that the composite
fermion picture explains the small magic numbers well, while a simple
geometrical picture does better as the magic number increases. Combination of
these two pictures leads to identification of all the magic numbers. Relation
of the magic-number states to the Wigner crystal and the fractional quantum
Hall state is discussed.Comment: 12 pages, 9 Postscript figures, uses jpsj.st
Localization from sigma-model geodesics
We use a novel method based on the semi-classical analysis of sigma-models to
describe the phenomenon of strong localization in quasi one-dimensional
conductors, obtaining the full distribution of transmission eigenvalues. For
several symmetry classes, describing random superconducting and chiral
Hamiltonians, the target space of the appropriate sigma-model is a (super)group
manifold. In these cases our approach turns out to be exact. The results offer
a novel perspective on localization.Comment: Published versio
Quantum dot to disordered wire crossover: A complete solution in all length scales for systems with unitary symmetry
We present an exact solution of a supersymmetric nonlinear sigma model
describing the crossover between a quantum dot and a disordered quantum wire
with unitary symmetry. The system is coupled ideally to two electron reservoirs
via perfectly conducting leads sustaining an arbitrary number of propagating
channels. We obtain closed expressions for the first three moments of the
conductance, the average shot-noise power and the average density of
transmission eigenvalues. The results are complete in the sense that they are
nonperturbative and are valid in all regimes and length scales. We recover
several known results of the recent literature by taking particular limits.Comment: 4 page
Magnetolocalization in disordered quantum wires
The magnetic field dependent localization in a disordered quantum wire is
considered nonperturbatively.
An increase of an averaged localization length with the magnetic field is
found, saturating at twice its value without magnetic field.
The crossover behavior is shown to be governed both in the weak and strong
localization regime by the magnetic diffusion length L_B. This function is
derived analytically in closed form as a function of the ratio of the mean free
path l, the wire thickness W, and the magnetic length l_B for a two-dimensional
wire with specular boundary conditions, as well as for a parabolic wire. The
applicability of the analytical formulas to resistance measurements in the
strong localization regime is discussed. A comparison with recent experimental
results on magnetolocalization is included.Comment: 22 pages, RevTe
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