Critical currents, grain boundaries and squids in the high temperature cuprate superconductors

A summary of some of the recent findings on the properties of grain boundaries in the high temperature superconductors, particularly in the Y1Ba2Ca3O7-δ epitaxial films, is presented. We show that some aspects of the behavior of the critical current across the grain boundary can be explained by assuming that the boundary can be presented by a dirty metal. Annealing in ozone at low temperatures decreases both the resistance and 1/f noise of the boundary; implying that the boundary contains charge trapping sites. Finally, the utility of single grain boundary junctions as Josephson elements of a SQUID is described. © 1991.