A comprehensive understanding of the transport properties of interfaces in high-Tc
cuprates been obtained by considering their microstructure, the possibility of bending of the electronic
band structure in these materials, and the predominant dx
2 -symmetry of the order parameter in most high-Tc
cuprates. These factors are of central importance for the critical current density and the normal state resistivity of grain boundaries and their dependencies on boundary misorientation and on applied magnetic and electrical fields. In addition, some of these factors play an important role for the transport properties of other interfaces involving high-Tc
superconductors, such as superconductors-normal metal contacts.
Based on the improved understanding of the mechanisms controlling interface transport properties, we have been able to meet a long-standing challenge in high-Tc
superconductivity and have increased the critical current densities of grain boundaries by large factors, using appropriate doping.