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 inferred that volume pinning centers play a dominant role on the basis of the law for the pinning force. analysing the forces acting on the flux line in the critical state, we suggest that the Lorentz force is not 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.