ANISOTROPIC CRITICAL-CURRENT DENSITY AND CROSSOVER OF SINGLE-COLLECTIVE VORTEX PINNING IN EPITAXIAL YBA2CU3O7-DELTA THIN-FILM

We have measured the critical current density, J(c), of c-axis-oriente d epitaxial YBa2Cu3O7-delta thin film as a function of applied field a nd angles. The results showed that two peaks of critical current densi ties were observed near theta = 0 degrees (or 180 degrees) and near 90 degrees, and there was deviation from theta = 0 degrees for the peak near 0 degrees and from theta = 90 degrees for the J(c) peaks near 90 degrees with the decrease of applied field, respectively. A crossover from single vortex pinning to collective pinning was also observed. Th e possible mechanisms of vortex pinning were discussed. Copyright (C) 1996 Elsevier Science Ltd.