Mechanisms Determining the Critical Current in Hard Superconductors

Abstract

It is well established that critical current densities in hard superconductors depend on pinning of the fluxoid lattice by microstructural inhomogeneities against electromagnetic forces. However, the connection between the measured critical current densities which are continuum quantities and the interactions between the pinning objects and the fluxoid lattice which are virtual point interactions has presented a rather complex problem that is the focus of this review. An experimental approach to diagnosis of the mechanisms and a rather general phenomenological theory are described and illustrated by a summary of some studies of hard superconductors containing high lattice-dislocation densities that provide a high density of rather weak pinning objects. Conclusions of general applicability are summarized.