2,973 research outputs found
Ergodicity and mixing bounds for the Fisher-Snedecor diffusion
We consider the Fisher-Snedecor diffusion; that is, the Kolmogorov-Pearson
diffusion with the Fisher-Snedecor invariant distribution. In the nonstationary
setting, we give explicit quantitative rates for the convergence rate of
respective finite-dimensional distributions to that of the stationary
Fisher-Snedecor diffusion, and for the -mixing coefficient of this
diffusion. As an application, we prove the law of large numbers and the central
limit theorem for additive functionals of the Fisher-Snedecor diffusion and
construct -consistent and asymptotically normal estimators for the
parameters of this diffusion given its nonstationary observation.Comment: Published in at http://dx.doi.org/10.3150/12-BEJ453 the Bernoulli
(http://isi.cbs.nl/bernoulli/) by the International Statistical
Institute/Bernoulli Society (http://isi.cbs.nl/BS/bshome.htm
Fluctuations of the Josephson current and electron-electron interactions in superconducting weak links
We derive a microscopic effective action for superconducting contacts with
arbitrary transmission distribution of conducting channels. Provided
fluctuations of the Josephson phase remain sufficiently small our formalism
allows to fully describe fluctuation and interaction effects in such systems.
As compared to the well studied tunneling limit our analysis yields a number of
qualitatively new features which occur due to the presence of subgap Andreev
bound states in the system. We investigate the equilibrium supercurrent noise
and evaluate the electron-electron interaction correction to the Josephson
current across superconducting contacts. At T=0 this correction is found to
vanish for fully transparent contacts indicating the absence of Coulomb effects
in this limit.Comment: 12 pages, 4 figure
Transport and magnetization dynamics in a superconductor/single-molecule magnet/superconductor junction
We study dc-transport and magnetization dynamics in a junction of arbitrary
transparency consisting of two spin-singlet superconducting leads connected via
a single classical spin precessing at the frequency . The presence of
the spin in the junction provides different transmission amplitudes for spin-up
and spin-down quasiparticles as well as a time-dependent spin-flip transmission
term. For a phase biased junction, we show that a steady-state superconducting
charge current flows through the junction and that an out-of-equilibrium
circularly polarized spin current, of frequency , is emitted in the
leads. Detailed understanding of the charge and spin currents is obtained in
the entire parameter range. In the adiabatic regime,
where is the superconducting gap, and for high transparencies of the
junction, a strong suppression of the current takes place around \vp \approx
0 due to an abrupt change in the occupation of the Andreev bound-states. At
higher values of the phase and/or precession frequency, extended
(quasi-particle like) states compete with the bound-states in order to carry
the current. Well below the superconducting transition, these results are shown
to be weakly affected by the back-action of the spin current on the dynamics of
the precessing spin. Indeed, we show that the Gilbert damping due to the
quasi-particle spin current is strongly suppressed at low-temperatures, which
goes along with a shift of the precession frequency due to the condensate. The
results obtained may be of interest for on-going experiments in the field of
molecular spintronics.Comment: 19 pages, 13 figures (v3) Minor modifications per referee's comments.
No change in results. (v2) 2 authors added, 1 reference added (Ref. 25), no
change in the text and result
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
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
On the Selfconsistent Theory of Josephson Effect in Ballistic Superconducting Microconstrictions
The microscopic theory of current carrying states in the ballistic
superconducting microchannel is presented. The effects of the contact length L
on the Josephson current are investigated. For the temperatures T close to the
critical temperature T_c the problem is treated selfconsistently, with taking
into account the distribution of the order parameter inside the
contact. The closed integral equation for in strongly inhomogeneous
microcontact geometry ( is the coherence length at
T=0) replaces the differential Ginzburg-Landau equation. The critical current
is expressed in terms of solution of this integral equation. The
limiting cases of and are considered. With
increasing length L the critical current decreases, although the ballistic
Sharvin resistance of the contact remains the same as at L=0. For ultra short
channels with ( is
the Debye frequency) the corrections to the value of critical current I_c(L=0)
are sensitive to the strong coupling effects.Comment: 15 pages LaTex, 3 jpg figure
Josephson effect in graphene SBS junctions
We study Josephson effect in graphene superconductor- barrier- superconductor
junctions with short and wide barriers of thickness and width , which
can be created by applying a gate voltage across the barrier region. We
show that Josephson current in such graphene junctions, in complete contrast to
their conventional counterparts, is an oscillatory function of both the barrier
width and the applied gate voltage . We also demonstrate that in the
thin barrier limit, where and keeping
finite, such an oscillatory behavior can be understood in terms of transmission
resonance of Dirac-Bogoliubov-de Gennes quasiparticles in superconducting
graphene. We discuss experimental relevance of our work.Comment: 7 Pg., 6 Figs, extended version submitted to PR
Voltage dependent conductance and shot noise in quantum microconstriction with single defects
The influence of the interference of electron waves, which are scattered by
single impurities and by a barrier on nonlinear conductance and shot noise of
metallic microconstriction is studied theoretically. It is shown that the these
characteristics are nonmonotonic functions on the applied bias.Comment: 18 pages,5 figure
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