TWIN BOUNDARY FLUX PINNING IN A HIGH-TC SUPERCONDUCTOR

The pinning potential due to a twin boundary in an anisotropic, continuous superconductor is calculated in a simple model. The model assumes the twin boundary to constitute a thin superconducting slab, different from and embedded in the host superconductor. Flux pinning is found to originate from two sources in several instances. One is an absolute minimum of the free energy. This type of pinning occurs when the twin boundary slab penetration length is larger than that of the host (weak link). The second pinning source is a surface barrier (local minimum in the free energy) at the interface of two superconductors. This barrier depends, in certain limits, very strongly on the twin boundary thickness and the anisotropy of the host superconductor. The model yields an estimate for the critical current parallel to the twin boundary.