Relaxation of superflow in a network: an application to the dislocation model of supersolidity of helium crystals

We have considered the dislocation network model for the supersolid state in He-4 crystals. In difference with uniform 2D and 3D systems, the temperature of superfluid transition T_c in the network is much smaller than the degeneracy temperature T_d. It is shown that a crossover into a quasi superfluid state occurs in the temperature interval between T_c and T_d. Below the crossover temperature the time of decay of the flow increases exponentially under decrease of the temperature. The crossover has a continuous character and the crossover temperature does not depend on the density of dislocations.Comment: Corrected typo

Charge ordering and interlayer phase coherence in quantum Hall superlattices

The possibility of the existence of states with a spontaneous interlayer phase coherence in multilayer electron systems in a high perpendicular to the layers magnetic field is investigated. It is shown that phase coherence can be established in such systems only within individual pairs of adjacent layers, while such coherence does not exist between layers of different pairs. The conditions for stability of the state with interlayer phase coherence against transition to a charge-ordered state are determined. It is shown that in the system with the number of layers N\leq 10 these conditions are satisfied at any value of the interlayer distance d. For N>10 there are two intervals of stability: at sufficiently large and at sufficiently small d. For N\to \infty the stability interval in the region of small d vanishesComment: 10 page

Resonant effects in the strongly driven phase-biased Cooper-pair box

We study the time-averaged upper level occupation probability in a strongly driven two level system, particularly its dependence on the driving amplitude, frequency and the energy level separation. In contrast to the case of weak driving, when the positions of the resonances almost do not depend on the driving amplitude, in the case of the strong diving their positions are strongly amplitude-dependent. We study these resonances in the concrete system -- the strongly driven phase-biased Cooper-pair box, which is considered to be weakly coupled to the tank circuit

Impurity induced bound states and proximity effect in a bilayer exciton condensate

The effect of impurities which induce local interlayer tunneling in bilayer exciton condensates is discussed. We show that a localized single fermion bound state emerges inside the gap for any strength of impurity scattering and calculate the dependence of the impurity state energy and wave function on the potential strength. We show that such an impurity induced single fermion state enhances the interlayer coherence around it, and is similar to the superconducting proximity effect. As a direct consequence of these single impurity states, we predict that a finite concentration of such impurities will increase the critical temperature for exciton condensation.Comment: 4 pages, 2 figure

Josephson and spontaneous currents at the interface between two d-wave superconductors with transport current in the banks

A stationary Josephson effect in the ballistic contact of two d-wave superconductors with different axes orientation and with tangential transport current in the banks is considered theoretically. We study the influence of the transport current on the current-phase dependence for the Josephson and tangential currents at the interface. It is demonstrated that the spontaneous surface current at the interface depends on the transport current in the banks due to the interference of the angle-dependent current-carrying condensate wave functions of the two superconductors.Comment: to be published in Fiz. Nizk. Temp. (Sov. J. Low Temp. Phys.), Vol.30, No.3 (2004