1,753 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
Fiske Steps and Abrikosov Vortices in Josephson Tunnel Junctions
We present a theoretical and experimental study of the Fiske resonances in
the current-voltage characteristics of "small" Josephson junctions with
randomly distributed misaligned Abrikosov vortices. We obtained that in the
presence of Abrikosov vortices the resonant interaction of electromagnetic
waves, excited inside a junction, with the ac Josephson current manifests
itself by Fiske steps in a current-voltage characteristics even in the absence
of external magnetic field. We found that the voltage positions of the Fiske
steps are determined by a junction size, but the Fiske step magnitudes depend
both on the density of trapped Abrikosov vortices and on their misalignment
parameter. We measured the magnetic field dependence of both the amplitude of
the first Fiske step and the Josephson critical current of low-dissipative
small based Josephson tunnel junctions with artificially introduced
Abrikosov vortices. A strong decay of the Josephson critical current and a weak
non-monotonic decrease of the first Fiske step amplitude on the Abrikosov
vortex density were observed. The experimentally observed dependencies are well
described by the developed theory.Comment: 21 pages, 7 figures, submitted to Physical Review
Magnetic field of Josephson vortices outside superconductors
We consider the structure of Josephson vortices approaching the junction
boundary with vacuum in large area Josephson junctions with the Josephson
length large relative to the London penetration depth .
Using the stability argument for one-dimentional solitons with respect to 2D
perturbations, it is shown that on the scale the Josephson vortices
do not spread near the boundary in the direction of the junction. %, which is
in a striking difference with behavior of Abrikosov vortices exiting
superconductors. The field distribution in vacuum due to the Josephson vortex
is evaluated, the information needed for the Scanning SQUID Microscopy.Comment: 5 RevTeX pages, 3 eps figures. The second version includes more
detailed explanations and corrections, and slightly modified figure
MgB2 radio-frequency superconducting quantum interference device prepared by atomic force microscope lithography
A new method of preparation of radio-frequency superconducting quantum
interference devices on MgB2 thin films is presented. The variable-thickness
bridge was prepared by a combination of optical lithography and of the
scratching by an atomic force microscope. The critical current of the
nanobridge was 0.35 uA at 4.2 K. Non-contact measurements of the current-phase
characteristics and of the critical current vs. temperature have been
investigated on our structures.Comment: RevTeX4. Accepted in Appl. Phys. Let
Classical-to-stochastic Coulomb blockade cross-over in aluminum arsenide wires
We report low-temperature differential conductance measurements in aluminum
arsenide cleaved-edge overgrown quantum wires in the pinch-off regime. At zero
source-drain bias we observe Coulomb blockade conductance resonances that
become vanishingly small as the temperature is lowered below . We
show that this behavior can be interpreted as a classical-to-stochastic Coulomb
blockade cross-over in a series of asymmetric quantum dots, and offer a
quantitative analysis of the temperature-dependence of the resonances
lineshape. The conductance behavior at large source-drain bias is suggestive of
the charge density wave conduction expected for a chain of quantum dots.Comment: version 2: new figure 4, refined discussio
Conductance of a STM contact on the surface of a thin film
The conductance of a contact, having a radius smaller than the Fermi wave
length, on the surface of a thin metal film is investigated theoretically. It
is shown that quantization of the electron energy spectrum in the film leads to
a step-like dependence of differential conductance G(V) as a function of
applied bias eV. The distance between neighboring steps in eV equals the energy
level spacing due to size quantization. We demonstrate that a study of G(V) for
both signs of the voltage maps the spectrum of energy levels above and below
Fermi surface in scanning tunneling experiments.Comment: 15 pages, 5 figure
Single-dopant resonance in a single-electron transistor
Single dopants in semiconductor nanostructures have been studied in great
details recently as they are good candidates for quantum bits, provided they
are coupled to a detector. Here we report coupling of a single As donor atom to
a single-electron transistor (SET) in a silicon nanowire field-effect
transistor. Both capacitive and tunnel coupling are achieved, the latter
resulting in a dramatic increase of the conductance through the SET, by up to
one order of magnitude. The experimental results are well explained by the rate
equations theory developed in parallel with the experiment.Comment: 16 pages, 8 figure
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