Yu.A. Genenko

Current-induced decoupling of superconducting planes in oriented YBaCuO thick films

Abstract The critical current of decoupling of superconducting CuO 2 planes is extracted from resistive data obtained on oriented YBaCuO films. Distinctive 3D—2D crossover in dissipation takes place at a temperature dependent current j c ( T ) that exhibits a clear tendency to vanish at T KT (Kosterlitz—Thouless transition temperature) of individual superconducting layers. That confirms the idea of full suppression of interlayer coupling due to 2D-vortex fluctuations close to T KT .

Controllable dimensional crossover of magnetic behavior in single- crystal GdBaCuO with variable oxygen content

Abstract Superconducting properties of GdBa 2 Cu 3 O 6+ δ single crystals of tetragonal symmetry are studied at various oxygen contents ( δ =0.2; 0.4; 0.56; 0.75). It is shown that transition from three-dimensional behavior to quasi-2D and further to strong two- dimensional behavior occurs as oxygen content is reduced. For the first time the single crystal of oxygen-deficient 1-2-3 is found to demonstrate the strong 2D-behavior expected of a stack of ultrathin films with no coupling between them. The superconducting transition in the samples with quasi-two-dimensional behavior is found to have features of a Berezinskii- Kosterlitz-Thouless transition. Fluctuations of the order parameter in the vicinity of the transition temperature change their dimensionality from 3D to 2D while oxygen content decreases.

Squeezed vortex in a layered structure of type-II superconductors

Abstract London approximation is used to solve the problem of magnetic vortex destroying order parameter in a superconducting layer of arbitrary thickness embedded between bulk superconducting screens. Like the well-known 2D-vortices in layered superconductors, the vortices under consideration interact logarithmically at large distances and carry magnetic flux θ θ 0 , the unit flux quantum. The stability of long vortices in a layered superconductor is discussed with respect to the decay of shorter vortices.

Suppression of the critical current of strongly anisotropic layered superconductors by 2D-vortex fluctuations

Abstract It is shown that the two-dimensional scenario of resistive behavior of the strongly anisotropic layered superconductors may take place due to the suppression of Josephson interlayer coupling by the vortex pairs, which removes the problem of Josephson confinement of 2D-vortices. The critical current is evaluated beyond the fluctuation region.

Helical magnetic vortex in a type-II superconductor: An exact solution of an edge barrier problem

Abstract An exact solution of problem of magnetic helical vortex entry into a long superconducting (SC) cylinder through a surface Bean-Livingston barrier is found in London approximation. Gibbs energy of system is calculated when transport current and longitudinal magnetic field are applied. A critical current of spontaneous vortex penetration into SC is found and compared to the critical current of left-handed helical instability.

Relaxation of magnetic vortex rings in a superconducting cylinder: some universal features

Abstract In the London approximation an exact solution for a magnetic vortex ring in a long superconducting cylinder of arbitrary thickness is found. The nonlinear equation of motion of the contracting vortex ring is solved exactly with regard to viscosity and inertial vortex mass. The solution of this equation exhibits some universal qualities of vortex ring motion.

Noise anomalies in small tunnel junctions at low temperatures

Abstract The discreteness of the carriers energy spectrum in small tunnel junctions is shown to cause the anomalous dependence of noise power on temperature S (ω)∼ T -1 at low temperatures instead of the proportionality predicted by the Nyquist formula. The effect manifest itself in the second order of the expansion in powers of the tunnel barrier transparency.

Exact calculation of the current in the tunnel Hamiltonian method

A method is proposed for going over from the nonequilibrium formulation to the thermal Greens function technique in the tunnel model. The method is used to obtain an exact solution for the current and the radius of convergence of the series of perturbation theory with respect to the transparency. The divergence of the series is found to be related to the rearrangement of the spectrum in sufficiently transparent tunnel junctions.