Recent developments in flux pinning

Considerable progress has recently been made regarding two fundamental aspects of flux pinning. A microscopic basis has been given for the elementary interaction potential of defects which are predominantly characterised by their electron scattering cross section. As a result new expressions have been derived for pinning by voids or bubbles, precipitates, and grain boundaries. Secondly, the puzzling threshold paradox for a system of weak, random pins has been resolved by the concept of collective pinning. The central issue of this concept is the positional disorder of the vortex lattice created by the interaction with the pinning centers. The relation between disorder, pin strength, pin density and bulk pinning force is better understood and may allow an estimate for the upper bounds of the critical current. These developments are briefly reviewed in this paper both regarding the theoretical background and their experimental verification.