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 $\beta$-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 $P$-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