Mechanisms for enhanced supercurrent across meandered grain boundaries in high-temperature superconductors

It has been well established that the critical current density J(c) across grain boundaries (GBs) in high-temperature superconductors decreases exponentially with misorientation angle theta beyond similar to 2 degrees-3 degrees. This rapid decrease is due to a suppression of the superconducting order parameter at the grain boundary, giving rise to weakly pinned Abrikosov-Josephson (AJ) vortices. Here we show that if the GB plane meanders, this exponential dependence no longer holds, permitting greatly enhanced Jc values: up to six times at 0 T and four times at 1 T at theta similar to 4 degrees-6 degrees. This enhancement is due to an increase in the current-carrying cross section of the GBs and the appearance of short AJ vortex segments in the GB plane, confined by the interaction with strongly pinned Abrikosov (A) vortices in the grains. (C) 2007 American Institute of Physics.