Interfaces in high-temperature superconductors

Abstract

After the discovery of high-temperature superconductors (HTS) five years ago, it soon became apparent that their interfacial characteristics would play an extremely important role in any foreseeable applications of these materials. In recent commercial devices, the weak-link characteristics of grain boundaries (GBs) have in fact been exploited to manufacture Josephson junction SQUIDS. On the other hand, the low critical current density of HTS is a considerable limitation for practical applications of the zero-resistance property, particularly in bulk materials. The weak-link behavior of GBs is largely responsible for this, but other types of interfaces such as those formed by metallic contacts or the interfaces between the substrate and a HTS thin film are also critical to the application of these materials. We shall review here some of the important interface issues that have been addressed by TEM techniques, but shall focus largely on the connection between the critical current (Jc) that can be transported across a grain boundary and its atomic-scale structure and composition.