3,339 research outputs found
Time dependent London approach, dissipation due to out-of-core normal excitations by moving vortices
The dissipative currents due to normal excitations are included in the London
description. The resulting time dependent London equations are solved for a
moving vortex and a moving vortex lattice. It is shown that the field
distribution of a moving vortex looses it cylindrical symmetry, it experiences
contraction which is stronger in the direction of the motion, than in the
direction normal to the velocity .
The London contribution of normal currents to dissipation is small relative
to the Bardeen-Stephen core dissipation at small velocities, but approaches the
latter at high velocities, where this contribution is no longer proportional to
. To minimize the London contribution to dissipation, the vortex lattice
orients as to have one of the unit cell vectors along the velocity, the effect
seen in experiments and predicted within the time-dependent Ginzburg-Landau
theory.Comment: 6 pages, 5 figure
Effect of fluctuations on vortex lattice structural transitions in superconductors
The rhombic-to-square transition field for cubic and tetragonal
materials in fields along [001] is evaluated using the nonlocal London theory
with account of thermal vortex fluctuations. Unlike extended Ginzburg-Landau
models, our approach shows that the line and the upper critical
field do not cross due to strong fluctuations near
which suppress the square anisotropy induced by the nonlocality. In increasing
fields, this causes re-entrance of the rhombic structure in agreement with
recent neutron scattering data on borocarbides.Comment: 4 pages, 2 figure
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