10 research outputs found
Onset of Vortices in Thin Superconducting Strips and Wires
Spontaneous nucleation and the consequent penetration of vortices into thin
superconducting films and wires, subjected to a magnetic field, can be
considered as a nonlinear stage of primary instability of the current-carrying
superconducting state. The development of the instability leads to the
formation of a chain of vortices in strips and helicoidal vortex lines in
wires. The boundary of instability was obtained analytically. The nonlinear
stage was investigated by simulations of the time-dependent generalized
Ginzburg-Landau equation.Comment: REVTeX 3.0, 12 pages, 5Postscript figures (uuencoded). Accepted for
Phys. Rev.
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
Nonequilibrium relaxation in neutral BCS superconductors: Ginzburg-Landau approach with Landau damping in real time
We present a field-theoretical method to obtain consistently the equations of
motion for small amplitude fluctuations of the order parameter directly in real
time for a homogeneous, neutral BCS superconductor. This method allows to study
the nonequilibrium relaxation of the order parameter as an initial value
problem. We obtain the Ward identities and the effective actions for small
phase the amplitude fluctuations to one-loop order. Focusing on the
long-wavelength, low-frequency limit near the critical point, we obtain the
time-dependent Ginzburg-Landau effective action to one-loop order, which is
nonlocal as a consequence of Landau damping. The nonequilibrium relaxation of
the phase and amplitude fluctuations is studied directly in real time. The
long-wavelength phase fluctuation (Bogoliubov-Anderson-Goldstone mode) is
overdamped by Landau damping and the relaxation time scale diverges at the
critical point, revealing critical slowing down.Comment: 31 pages 14 figs, revised version, to appear in Phys. Rev.
Effect of ordered array of magnetic dots on the dynamics of Josephson vortices in stacked SNS Josephson junctions under DC and AC current
THEORY OF THE PHASE-SLIP STATE IN SUPERCONDUCTING FILAMENTS
Une généralisation de l'équation de Ginzburg-Landau dépendante du temps, qui était dérivée autrefois pour des supraconducteurs sales près de Tc, a des solutions oscillantes avec des glisssements de phase au-dessous et au-dessus du courant critique pour des fils fins et homogènes. Nous discutons la stabilité des différentes solutions. Les résultats sont comparés avec les caractéristiques courant-tension trouvées dans des whiskers et micro-ponts et avec la structure correspondant à des centres de glissements de phase observée récemment.A previously derived generalized time-dependent Ginzburg-Landau equation valid for dirty superconductors in the vicinity of Tc exhibits for thin homogeneous filaments oscillatory phase-slip solutions below and above the critical depairing current. The stability of the various solutions is discussed. The results are compared with I-V curves found experimentally in whiskers and microbridges and with the structure of a phase-slip center observed recently
Condition for the occurrence of phase slip centers in superconducting nanowires under applied current or voltage
The damping of a quartz tuning fork in superfluid He-3-B at low temperatures
We have measured the damping on a quartz tuning fork in the B-phase of superfluid He-3 at low temperatures, below 0.3T (c). We present extensive measurements of the velocity dependence and temperature dependence of the damping force. At the lowest temperatures the damping is dominated by intrinsic dissipation at low velocities. Above some critical velocity an extra temperature independent damping mechanism quickly dominates. At higher temperatures there is additional damping from thermal quasiparticle excitations. The thermal damping mechanism is found to be the same as that for a vibrating wire resonator; Andreev scattering of thermal quasiparticles from the superfluid back-flow leads to a very large damping force. At low velocities the thermal damping force varies linearly with velocity, but tends towards a constant at higher velocities. The thermal damping fits very well to a simple model developed for vibrating wire resonators. This is somewhat surprising, since the quasiparticle trajectories through the superfluid flow around the fork prongs are more complicated due to the relatively high frequency of motion. We also discuss the damping mechanism above the critical velocity and compare the behaviour with other vibrating structures in superfluid He-3-B and in superfluid He-4 at low temperatures. In superfluid He-4 the high velocity response is usually dominated by vortex production (quantum turbulence), however in superfluid He-3 the response may either be dominated by pair-breaking or by vortex production. In both cases the critical velocity in superfluid He-3-B is much smaller and the high velocity drag coefficient is much larger, compared to equivalent measurements in superfluid He-4