S.N. Artemenko

Vortex motion and kosterlitz-thouless transition in superconducting single crystals Bi2Sr2CaCu2Ox

Abstract Hall voltages VH in a resistive superconducting state and in a normal state are shown to have opposite signs. This is accounted for by a flux vortex motion. Current-voltage characteristics V∝Ia(T) near the transition with a characteristic Nelson-Kosterlitz jump in a(T) at T = Tc present the evidence for a Kosterlitz-Thouless (KT) transition, which may be explained by flux vortex unbinding inside the superconducting planes.

Magnetoresistance of a layered high-Tc superconductor below the Berezinskii-Kosterlitz-Thouless transition

Abstract The mechanism of the resistivity of a weakly coupled layered supecocoductor below the Berezinskii-Kosterlitz-Thouless (BKT)_ transition temperature T BKT in a magnetic field perpendicular to the layers is studied experimentally and theoretically. The resistance of Bi 2 Sr 2 CaCu 2 O x single crystals at temperatures 70–90 K in a magnetic field H T T BKT in a field H larger than 10–30 Oe the resistance is characterized by the thermoactivated behaviour down to some characteristic temperature T ∗ (H) , below which power-law I − V curves V ∝ I aH( T )+1 were observed. We account for these results by the creation of 2D-vortices due to the breaking of Abrikosov vortex lines by thermal fluctuations and transport current. Calculated dependences of the power index a H on the temperature and magnetic field agree with the experimental ones. The observed T ∗ (H) dependence is described by the condition that the mean thermal fluctuations of the positions of the 2D-vortices forming flux lines are of the order of a mean distance between flux lines.

Stability, collective modes and radiation from sliding Josephson vortex lattice in layered superconductors

We calculate collective modes and study stability of the flux-flow regime of the Josephson vortex lattice driven by a transport current perpendicular to the conducting layers of a layered superconductor in the limits of high and low magnetic fields. The sliding triangular vortex lattice is found to be stable at small velocities up to a critical value. At larger velocities the uniform motion of neither triangular nor quadrangular vortex lattice is stable. In the flux-flow regime we calculate intensity of the radiation emitted from a semi-infinite sample. The radiation power exhibits a large maximum at the lattice velocities corresponding to the Josephson plasma frequency. However, this maximum can be observed only in large enough magnetic field. We demonstrate that the convective term in the equation of motion for the lattice displacement that was reported to be responsible for dynamical phase transitions is small in high magnetic field.

Collective modes in layered superconductors

Weakly damped collective oscillations in layered superconductors are examined theoretically. The calculation is based on kinetic equations for Green functions generalized to the case of layered superconductors with weak interlayer coupling. We show that weakly damped plasma oscillations of superconducting electrons can exist in such superconductors and calculate the spectrum of the mode. The oscillations are reminiscent of Josephson plasma oscillations in a superconducting tunnel junction. As the temperature approaches the critical one, these oscillations transform into Carlson-Goldman modes. Possibilities for detecting the plasma mode experimentally are discussed. We found distinctive features in the reflection coefficient for an electromagnetic wave incident at an arbitrary angle on a plane parallel to the layers. The presence of the mode changes also the dispersion relation for the waves propagating along a thin film of a layered superconductor.

TWO-DIMENSIONAL BEHAVIOUR OF LAYERED HIGH-Tc SUPERCONDUCTORS

High-Tc superconductors (HTSs) have a layered structure, which strongly affects their physics. Bulk crystals exhibit the two-dimensional (2D) behaviour typical for superconducting films of atomic thickness. Fluctuation contribution to conductivity above mean-field critical temperature Tc0 is characteristic to 2D superconductors. Finite resistivity in layered HTSs appears above Berezinskii-Kosterlitz-Thouless (BKT) transition Tc, which is by several degrees smaller than Tc0. Below Tc power-law I-V curves are observed. The transition and its main manifestations are described as a result of thermal creation of 2D-vortices with cores residing inside single superconducting layers. Magnetoresistive effects near the BKT transition are discussed briefly.

Effect of thermal and quantum fluctuations on superfluid density in layered superconductors

Abstract We calculate suppression of inter- and intra-layer superconducting currents due to equilibrium phase fluctuations and find that, in contrast to a recent prediction, the effect of thermal fluctuations cannot account for linear temperature dependence of the superfluid density in high- T c superconductors at low temperatures. Quantum fluctuations are found to dominate over thermal fluctuations at low temperatures due to hardening of their spectrum caused by the Josephson plasma resonance. Near T c sizeable thermal fluctuations are found to suppress the critical current in the stack direction stronger than in the direction along the layers. Fluctuations of quasi-particle branch imbalance make the spectral density of voltage fluctuations at small frequencies non-zero, in contrast to what may be expected from a naive interpretation of Nyquist formula.

On dissipation mechanism in the intrinsic Josephson effect in layered superconductors with d-wave pairing

Conductivity at low temperatures in the regime of the intrinsic Josephson effect in layered superconductors with d-wave pairing and coherent interlayer transfer is studied theoretically. Mechanism of the resistivity related to excitations of the quasiparticles via the d-wave gap is shown to describe main qualitative features of the effect observed at voltages smaller than the amplitude of the superconducting gap. Interaction of the Josephson junctions formed by the superconducting layers due to charging effects is found to be small.

Intrinsic Josephson effect in layered superconductors with d-wave pairing

Abstract The resistive state in layered d-wave superconductors is studied using the quasiclassical Greens function approach. Similarity with a stack of Josephson junctions is found at small voltages. In the spatially uniform state differential conductivity at higher voltages becomes negative. In the nonuniform state the branch imbalance violates the Josephson relation.

Linear and nonlinear AC response of Abrikosov vortices in layered superconductors adiabatic approximation

Abstract Linear and nonlinear AC responses for a magnetically coupled stack of two-dimensional vortices (2DVs) forming an Abrikosov vortex line perpendicular to the layers of a layered superconducting film are calculated. By solving the Fokker-Planck equations for the distribution functions of 2DV positions in the adiabatic approximation and including randomly distributed pinning centers, a nonlinear differential equation for the continuous shift function S ( z , t ) is derived. Josephson coupling only changes coefficients in this equation. The equation for S ( z , t ) is solved perturbatively for the linear AC response and for the third-order mixing current at frequency 2ω 1 -ω 2 . This pseudoharmonic mixing probes the nonlinearity of the intervortex force and its interplay with pinning. Explicit analytical results are given for the surface impedance Z s and the mixing current δ j ( 3 ). The cases of thin and thick films with respect to the AC penetration length are considered in detail.