Using large-scale simulations on parallel processors, we analyze
in detail the dynamical behavior of superconducting vortices
undergoing avalanches. In particular, we quantify the effect of
the pinning landscape on the macroscopic properties of vortex
avalanches and vortex plastic flow. These dynamical instabilities
are triggered when the external magnetic field is increased slightly,
and are thus driven by a flux gradient rather than by thermal effects.
The flux profiles, composed of rigid flux lines that interact with
100 or more vortices, are maintained in the Bean critical state
and do not decay away from it. By directly determining vortex
positions during avalanches in the plastically moving lattice, we
find that experimentally observable voltage bursts correspond to the
pulsing movement of vortices along branched channels or winding chains
in a mannger reminiscent of lightning strikes. This kind of motion
cannot be described by elastic theories. We relate
the velocity field and cumulative patterns of vortex flow channels with
statistical quantities, such as distributions of avalanche sizes.
Samples with a high density of strong pinning sites produce very broad
avalanche distributions. Easy-flow vortex channels appear in samples
with a low pinning density, and typical avalanche sizes emerge in
an otherwise broad distribution of sizes. We observe a crossover from
interstitial motion in narrow channels to pin-to-pin motion in
broad channels as pin density is increased.
MPEG Movie of vortex avalanches in a sample with strong pinning:
C. J. Olson, C. Reichhardt, and F. Nori,
Phys. Rev. B 56,
6175 (1997).
C. J. Olson, C. Reichhardt, J. Groth, S.B. Field, and F. Nori,
Physica C 290, 89 (1997).
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Last Modified: 10/31/07