4,240 research outputs found
Stability of dynamic coherent states in intrinsic Josephson-junction stacks near internal cavity resonance
Stacks of intrinsic Josephson junctions in the resistive state can by
efficiently synchronized by the internal cavity mode resonantly excited by the
Josephson oscillations. We study the stability of dynamic coherent states near
the resonance with respect to small perturbations. Three states are considered:
the homogeneous and alternating-kink states in zero magnetic field and the
homogeneous state in the magnetic field near the value corresponding to half
flux quantum per junction. We found two possible instabilities related to the
short-scale and long-scale perturbations. The homogeneous state in modulated
junction is typically unstable with respect to the short-scale alternating
phase deformations unless the Josephson current is completely suppressed in one
half of the stack. The kink state is stable with respect to such deformations
and homogeneous state in the magnetic field is only stable within a certain
range of frequencies and fields. Stability with respect to the long-range
deformations is controlled by resonance excitations of fast modes at finite
wave vectors and typically leads to unstable range of the wave-vectors. This
range shrinks with approaching the resonance and increasing the in-plane
dissipation. As a consequence, in finite-height stacks the stability frequency
range near the resonance increases with decreasing the height.Comment: 15 pages, 8 figures, to appear in Phys. Rev.
Conductance characteristics of current-carrying d-wave weak links
The local quasiparticle density of states in the current-carrying d-wave
superconducting structures was studied theoretically. The density of states can
be accessed through the conductance of the scanning tunnelling microscope. Two
particular situations were considered: the current state of the homogeneous
film and the weak link between two current-carrying d-wave superconductors.Comment: 4 pages, 3 figures; to appear in Low. Temp. Phy
Non-adiabatic Josephson Dynamics in Junctions with in-Gap Quasiparticles
Conventional models of Josephson junction dynamics rely on the absence of low
energy quasiparticle states due to a large superconducting gap. With this
assumption the quasiparticle degrees of freedom become "frozen out" and the
phase difference becomes the only free variable, acting as a fictitious
particle in a local in time Josephson potential related to the adiabatic and
non-dissipative supercurrent across the junction. In this article we develop a
general framework to incorporate the effects of low energy quasiparticles
interacting non-adiabatically with the phase degree of freedom. Such
quasiparticle states exist generically in constriction type junctions with high
transparency channels or resonant states, as well as in junctions of
unconventional superconductors. Furthermore, recent experiments have revealed
the existence of spurious low energy in-gap states in tunnel junctions of
conventional superconductors - a system for which the adiabatic assumption
typically is assumed to hold. We show that the resonant interaction with such
low energy states rather than the Josephson potential defines nonlinear
Josephson dynamics at small amplitudes.Comment: 9 pages, 1 figur
Phase diagram of geometric d-wave superconductor Josephson junctions
We show that a constriction-type Josephson junction realized by an epitactic
thin film of a d-wave superconductor with an appropriate boundary geometry
exhibits intrinsic phase differences between 0 and pi depending on geometric
parameters and temperature. Based on microscopic Eilenberger theory, we provide
a general derivation of the relation between the change of the free energy of
the junction and the current-phase relation. From the change of the free
energy, we calculate phase diagrams and discuss transitions driven by geometric
parameters and temperature.Comment: 9 pages, 11 figures. Phys. Rev. B, accepte
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
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
String Field Theory Vertices, Integrability and Boundary States
We study Neumann coefficients of the various vertices in the Witten's open
string field theory (SFT). We show that they are not independent, but satisfy
an infinite set of algebraic relations. These relations are identified as
so-called Hirota identities. Therefore, Neumann coefficients are equal to the
second derivatives of tau-function of dispersionless Toda Lattice hierarchy
(this tau-function is just the partition sum of normal matrix model). As a
result, certain two-vertices of SFT are identified with the boundary states,
corresponding to boundary conditions on an arbitrary curve. Such two-vertices
can be obtained by the contraction of special surface states with Witten's
three vertex. We analyze a class of SFT surface states,which give rise to
boundary states under this procedure. We conjecture that these special states
can be considered as describing D-branes and other non-perturbative objects as
"solitons" in SFT. We consider some explicit examples, one of them is a surface
states corresponding to orientifold.Comment: 28pages plus appendices, acknowledgments adde
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