Simple model for critical currents in anisotropic type-II superconductors.

Abstract

Recently, a continuum theory of the mixed state in type-II superconductors was developed by two of us (Mathieu and Simon). An unorthodox model for the critical currents in soft materials proceeded from this theory. We show that this surface pinning model can be easily extended to soft high-${\mathit{T}}_{\mathit{c}}$ superconductors (HTSC's). It successfully predicts the order of magnitude of critical currents such as observed in monocrystals or epitaxial films, and accounts for the existence and the position in the (H,T) plane of the irreversibility line. In the framework of our model, the vanishing of critical currents appears as a simple consequence of the strong anisotropy of HTSC's; there is no need for any bulk phase transition of the vortex array.