Critical Currents in [001] Grains and across Their Tilt Boundaries in YBa₂Cu₃O₇ Films

The temperature and magnetic field dependences of the critical-current density of superconducting YBa₂Cu₃O₇ films have been determined from transport measurements across individual [001] tilt boundaries and within single [001] grains. The results provide evidence that the basal-plane J_f is limited by flux creep. In contrast, the I-V characteristics and the temperature magnetic field dependences of the grain-boundary J_c are consistent with a superconductor-normal-superconductor-type weak-link behavior. These results imply that the transport properties of these materials can be treated within a BCS framework.