Magneto-optical study of twin boundary pinning in YBa 2Cu 3O 7-δ

Abstract

Using a high-resolution magneto-optical technique we studied the flux penetration and pinning in YBa 2Cu 3O 7-δ crystals in the presence of isolated twin boundaries. The most important factor determining the behavior of the twin boundaries is the direction of flux motion with respect to the boundary. Up to temperatures close to T c twin boundaries are effective barriers for flux motion transverse to the boundaries. For flux motion parallel to the boundary the characteristic “flame”-shaped flux patterns indicative of weak link behavior (i. e. low J c) of the boundary are observed.