Description of hysteretic current-voltage characteristics of SNS junctions

Simplified model for current-voltage characteristics of weak links is suggested. It is based on an approach considering the multiple Andreev reflection in metallic Josephson junction. The model allows to calculate current-voltage characteristics of the superconductor - normal metal - superconductor junctions with different thicknesses of normal layer at different temperatures. A hysteretic peculiarity of $V(I)$ dependence is described as result of the negative differential resistance. The current-voltage characteristic of high-$T_c$ composite YBCO +BaPbO${_3}$ were computed.Comment: 9 pages, 5 figures, submited to Supercond. Sci. Technol, replased Fig.5 for more correct comparison with experimen

Secondary peak on asymmetric magnetization loop of type-II superconductors

Asymmetric magnetization loops with a second peak effect were parameterized by the extended critical state model. The magnetic field distribution in a sample is considered. Expression is suggested for a peak of the critical current density and corresponding depression on field dependence of the depth of surface layer with equilibrium magnetization. These functions determine the width and the asymmetry of a magnetization loop. Asymmetry of the secondary peak height on magnetization branches for increasing and decreasing field is reproduced on the computed magnetization curves.Comment: 6 pages, 2 figures, Equation 6 is modified to be f=0 at B=

Characteristics of the electric field accompanying a longitudinal acoustic wave in a metal. Anomaly in the superconducting phase

The temperature dependence of the amplitude and phase of the electric potential arising at a plane boundary of a conductor when a longitudinal acoustic wave is incident normally on it is investigated theoretically and experimentally. The surface potential is formed by two contributions, one of which is spatially periodic inside the sample, with the period of the acoustic field; the second is aperiodic and arises as a result of an additional nonuniformity of the electron distribution in a surface layer of the metal. In the nonlocal region the second contribution is dominant. The phases of these contributions are shifted by approximately \pi /2. For metals in the normal state the experiment is in qualitative agreement with the theory. The superconducting transition is accompanied by catastrophically rapid vanishing of the electric potential, in sharp contrast to the theoretical estimates, which predict behavior similar to the BCS dependence of the attenuation coefficient for a longitudinal sound.Comment: 9 pages, 6 figure

Anisotropy and crystallite misalignment in textured superconductors

A misalignment of anisotropic crystallites causes small values of anisotropy and decreases the critical current density of textured polycrystalline superconductors. To relate the crystallite misalignment and out-plane anisotropy, the magnetic properties of the textured Bi2223 polycrystalline superconductor were investigated. A distribution of orientation angles of crystallites was determined using different data: scanning electron microscopy images and hysteresis magnetization loops when an external magnetic field was applied at different angles with respect to the texturing plane of the sample. It was demonstrated that the standard deviation of the distribution and the magnetic disorder angle of crystallites in textured samples can be determined from the magnetization data in perpendicular directions. These data may be either the irreversible magnetization measured for two different orientations of the sample or the simultaneously measured magnetization projections parallel and perpendicular to the magnetic field.Comment: 11 pages, 6 figure

Pinning Enhancement by Heterovalent Substitution in Y1−x_{1-x}REx_{x}Ba2_{2}Cu3_{3}O7−δ_{7-\delta}

The intragrain pinning in high-$T_c$ superconductor compounds Y$_{1-x}$RE$_{x}$Ba$_{2}$Cu$_{3}$O$_{7-\delta}$ with low concentration of RE (La, Ce, Pr) was investigated. Magnetic and transport measurements reveal that the pinning is maximal for the concentration of heterovalent RE such that the average distance between the impurity ions in the plane of rare-earth elements close to the diameter of Abrikosov vortices in YBCO.Comment: 11 pages, 6 figures, will be published in SUS