Pinning enhancement upon the magnetic flux trapping in the clusters of a normal phase with fractal boundaries

Abstract

The magnetic flux trapping in type-II superconductor containing fractal clusters of a normal phase, which act as pinning centers, is considered. The critical current distribution for an arbitrary fractal dimension of the boundaries of the normal phase clusters is obtained. It is revealed that the fractality of the cluster boundaries intensifies the pinning and thereby raises the critical current of a superconductor. The pinning gain coefficient as a function of critical current for different fractal dimensions is calculated.