WEAK LINK BEHAVIOR OF GRAIN-BOUNDARIES IN ND-BASED, BI-BASED, AND TL-BASED CUPRATE SUPERCONDUCTORS

We have studied single-grain-boundary junctions in the neodymium-, bismuth-, and thallium-based cuprate superconductors and find that they behave as weak links, qualitatively similar to the YBa2Cu3O7-delta superconductor. In general, the grain boundary critical current is determined by flux flow for small misorientation angles and by Josephson junction like coupling for large angles. The latter is verified by the observation of voltage oscillations with an external magnetic field in superconducting quantum interference devices built using single-grain-boundary junctions of these materials. The commonality of behavior of grain boundaries in all of the high temperature cuprate superconductors suggests that the weak link is most likely associated with the structure of the grain boundary and the evidence points increasingly to dislocations, which describe the topology of the boundary.