11 research outputs found
Rearrangement of the vortex lattice due to instabilities of vortex flow
With increasing applied current we show that the moving vortex lattice
changes its structure from a triangular one to a set of parallel vortex rows in
a pinning free superconductor. This effect originates from the change of the
shape of the vortex core due to non-equilibrium effects (similar to the
mechanism of vortex motion instability in the Larkin-Ovchinnikov theory). The
moving vortex creates a deficit of quasiparticles in front of its motion and an
excess of quasiparticles behind the core of the moving vortex. This results in
the appearance of a wake (region with suppressed order parameter) behind the
vortex which attracts other vortices resulting in an effective
direction-dependent interaction between vortices. When the vortex velocity
reaches the critical value quasi-phase slip lines (lines with fast vortex
motion) appear which may coexist with slowly moving vortices between such
lines. Our results are found within the framework of the time-dependent
Ginzburg-Landau equations and are strictly valid when the coherence length
is larger or comparable with the decay length of the
non-equilibrium quasiparticle distribution function. We qualitatively explain
experiments on the instability of vortex flow at low magnetic fields when the
distance between vortices . We speculate that a
similar instability of the vortex lattice should exist for even when
.Comment: 10 pages, 11 figure
AC Josephson properties of phase slip lines in wide tin films
Current steps in the current-voltage characteristics of wide superconducting
Sn films exposed to a microwave irradiation were observed in the resistive
state with phase slip lines. The behaviour of the magnitude of the steps on the
applied irradiation power was found to be similar to that for the current steps
in narrow superconducting channels with phase slip centers and, to some extent,
for the Shapiro steps in Josephson junctions. This provides evidence for the
Josephson properties of the phase slip lines in wide superconducting films and
supports the assumption about similarity between the processes of phase slip in
wide and narrow films.Comment: 7 pages, 2 figures, to be published in Supercond. Sci. Techno
Phase diagram of a current-carrying superconducting film in the absence of a magnetic field
We present the phase diagram for the current states of superconducting films,
based on the experimental investigation of the resistive transition induced by
transport current. We found that a rather narrow film never enters the vortex
state, but experiences direct transition from the purely superconducting state
to the resistive state with phase-slip centers as soon as the current exceeds
the Ginzburg-Landau critical current Ic. The Meissner current state of the
films of intermediate width transforms at I > 0.8Ic to the vortex resistive
state which exists within the current interval 0.8Ic < I < Im, where the value
Im of the upper critical current is in a good agreement with the theory. The
vortex state of wide films is realized within the current region I^{AL} < I <
Im, where I^{AL} is the transition point to the vortex state by Aslamazov and
Lempitskiy. At I>Im, the wide films enter a vortex-free resistive state with
phase-slip lines.Comment: 4 pages, 5 figure
Current states in superconducting films: Numerical results
We present numerical solutions of Aslamazov–Lempitskiy (AL) equations for distributions of the transport
current density in thin superconducting films in the absence of external magnetic field, in both the Meissner and
the vortex states. These solutions describe smooth transition between the regimes of a wide film and a narrow
channel and enable us to find critical currents and current-voltage characteristics within a wide range of the film
width and temperature. The normalized critical currents and the electric field were found to be universal functions
of the relation between the film width and the magnetic field penetration depth. We calculate the fitting
constants of the AL theory and propose approximating formulas for the current density distributions and critical
currents