The elastic Green's function for the pinned flux-line lattice in a type II superconductor
The elastic Green's function for the pinned flux-line lattice in the critical state is defined and evaluated in the coherent potential approximation. The presence of pinning sites contributes an additional restoring force, which must be calculated within a complete theory of the critical state, but which can be measured. Results are given for the dependence of the Green's function on the density of strong flux-line pins, and a criterion is derived for the applicability of the dilute-limit approximation. This criterion is never satisfied near the upper and lower critical fields. Assuming that the pins all interact sufficiently strongly with the flux-line lattice to exceed the threshold criterion, we find that the Green's function decreases (the flux-line lattice becomes more rigid) with increasing pin density.
KeywordsMagnetic Material Critical State Threshold Criterion Critical Field Complete Theory
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