3,784 research outputs found
Persistent Currents in Helical Structures
Recent discovery of mesoscopic electronic structures, in particular the
carbon nanotubes, made necessary an investigation of what effect may helical
symmetry of the conductor (metal or semiconductor) have on the persistent
current oscillations. We investigate persistent currents in helical structures
which are non-decaying in time, not requiring a voltage bias, dissipationless
stationary flow of electrons in a normal-metallic or semiconducting cylinder or
circular wire of mesoscopic dimension. In the presence of magnetic flux along
the toroidal structure, helical symmetry couples circular and longitudinal
currents to each other. Our calculations suggest that circular persistent
currents in these structures have two components with periods and
( is an integer specific to any geometry). However, resultant
circular persistent current oscillations have period.
\pacs{PACS:}PACS:73.23.-bComment: 4 pages, 2 figures. Submitted to PR
Malliavin calculus for difference approximations of multidimensional diffusions: truncated local limit theorem
For a difference approximations of multidimensional diffusion, the truncated
local limit theorem is proved. Under very mild conditions on the distribution
of the difference terms, this theorem provides that the transition
probabilities of these approximations, after truncation of some asymptotically
negligible terms, possess a densities that converge uniformly to the transition
probability density for the limiting diffusion and satisfy a uniform
diffusion-type estimates. The proof is based on the new version of the
Malliavin calculus for the product of finite family of measures, that may
contain non-trivial singular components. An applications for uniform estimates
for mixing and convergence rates for difference approximations to SDE's and for
convergence of difference approximations for local times of multidimensional
diffusions are given.Comment: 34 page
Josephson effect in ballistic graphene
We solve the Dirac-Bogoliubov-De-Gennes equation in an impurity-free
superconductor-normal-superconductor (SNS) junction, to determine the maximal
supercurrent that can flow through an undoped strip of graphene with heavily
doped superconducting electrodes. The result is determined by the
superconducting gap and by the aspect ratio of the junction (length L, small
relative to the width W and to the superconducting coherence length). Moving
away from the Dirac point of zero doping, we recover the usual ballistic result
in which the Fermi wave length takes over from L. The product of critical
current and normal-state resistance retains its universal value (up to a
numerical prefactor) on approaching the Dirac point.Comment: 4 pages, 2 figure
Supercurrent-phase relationship of a Nb/InAs(2DES)/Nb Josephson junction in overlapping geometry
Superconductor/normal conductor/superconductor (SNS) Josephson junctions with
highly transparent interfaces are predicted to show significant deviations from
sinusoidal supercurrent-phase relationships (CPR) at low temperatures. We
investigate experimentally the CPR of a ballistic Nb/InAs(2DES)/Nb junction in
the temperature range from 1.3 K to 9 K using a modified Rifkin-Deaver method.
The CPR is obtained from the inductance of the phase-biased junction. Transport
measurements complement the investigation. At low temperatures, substantial
deviations of the CPR from conventional tunnel-junction behavior have been
observed. A theoretical model yielding good agreement to the data is presented.Comment: RevTex4, 4 pages including 3 figure
- …