Pinning by the local changes of the electron mean free path in anisotropic type-II superconductors.

Abstract

The bulk pinning force density ${F}_{p}$ and the critical current ${j}_{c}$ of a dirty type-II superconductor, with spatially varying electron mean free path l along a given direction, are calculated using the Ginzburg-Landau-Abrikosov theory. In high fields the critical force density ${F}_{c}$ is proportional to (1-B/${B}_{c2}$${)}^{2}$(B/${B}_{c2}$${)}^{m}$, where 0<m<1, but depends also on the size and form of inhomogeneity (grain boundary, dislocation wall, etc.) which causes the change of l. This may explain deviations from straight lines in the ``Kramer plots'' of ${j}_{c}^{1/2}$${B}^{1/4}$ versus B/${B}_{c2}$ and the approximate scaling of ${F}_{c}$ when the temperature is changed.