7 research outputs found
Dynamics of 2D pancake vortices in layered superconductors
The dynamics of 2D pancake vortices in Josephson-coupled
superconducting/normal - metal multilayers is considered within the
time-dependent Ginzburg-Landau theory. For temperatures close to a
viscous drag force acting on a moving 2D vortex is shown to depend strongly on
the conductivity of normal metal layers. For a tilted vortex line consisting of
2D vortices the equation of viscous motion in the presence of a transport
current parallel to the layers is obtained. The specific structure of the
vortex line core leads to a new dynamic behavior and to substantial deviations
from the Bardeen-Stephen theory. The viscosity coefficient is found to depend
essentially on the angle between the magnetic field and the
axis normal to the layers. For field orientations close to the layers
the nonlinear effects in the vortex motion appear even for slowly moving vortex
lines (when the in-plane transport current is much smaller than the
Ginzburg-Landau critical current). In this nonlinear regime the viscosity
coefficient depends logarithmically on the vortex velocity .Comment: 15 pages, revtex, no figure
AC conductivity of a niobium thin film in a swept magnetic field
We report the results of the measurement the ac conductivity of a Nb
superconducting thin film in a swept dc magnetic field. In the mixed state the
swept dc field creates vortices at the film surface which pass through the film
and form the observed ac conductivity. Vortex rate generation does not depend
on the value of the dc field and there is a large plateau-like region of dc
magnetic fields where the dissipation is approximately constant. A proposed
phenomenological model describes quite well the main features of the ac
response in these fields including its dependency on the sweep rate, ac
amplitude, frequency, and value of the second and third harmonics.Comment: 7 pages and 10 figures; Journal of Physics: Condensed Matter, 201