OBSERVATION OF STRONG TO JOSEPHSON-COUPLED CROSSOVER IN 10 YBA2CU3OX BICRYSTAL JUNCTIONS

A temperature-dependent strong to weak (Josephson) coupling crossover near 75 K is observed for 10° misorientation YBa2Cu3Ox grain boundaries. Below 75 K the current–voltage characteristic (IVC) shows strongly coupled, flux-flow behavior. Above 75 K, the IVC is Josephson coupled. The data are consistent with a network of microbridges at the grain boundary defined by dislocation strain fields. The data are compared to recent calculations by A. Gurevich and A. E. Pashitskii [Phys. Rev. B 57, 13878 (1998)]. The characteristic voltages for these low-angle grain boundaries are higher than high-angle boundaries at 77 K, and could lead to improved high-temperature superconducting device operation in this temperature range.