46 research outputs found
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 dependence is
described as result of the negative differential resistance. The
current-voltage characteristic of high- composite YBCO +BaPbO 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 YREBaCuO
The intragrain pinning in high- superconductor compounds
YREBaCuO 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