THE CRITICAL-CURRENT DENSITY AND THE PINNING MECHANISM OF EPITAXIAL YBA2CU3O7-DELTA THIN-FILMS

The dependences of critical current density J(c) in the ab plane upon applied magnetic field H and the angle between the current I and H for YBa2Cu3O7-delta (YBCO) epitaxial thin film have been studied. It is i nferred that volume pinning centers play a dominant role on the basis of the law for the pinning force. analysing the forces acting on the f lux line in the critical state, we suggest that the Lorentz force is n ot the only driving force for the motion of flux lines. In the H // I case, the decrease of critical current density J(c) with increasing H is due to a suppression of the superconductivity by the applied field. The behavior of the critical current density can be well described by the anisotropic Kim-Anderson model.