Advances in high-Tc grain boundary junctions

We review results on two novel types of grain-boundary Josephson junctions in the high-critical-temperature cuprate superconductors. The quality of YBa(2)Cu(3)O(7-delta) biepitaxial grain-boundary Josephson junctions has been improved using a new growth geometry to the point that "tunnel-like" characteristics are reproducibly obtained. The consequent low barrier transmission probabilities are apparently favorable for isolating intrinsic d-wave induced effects. We also focus on peculiar aspects of spontaneous currents in HTS Josephson junctions, which are unique and reflect the intimate relation between vortex matter and the Josephson effect. Bicrystal grain-boundary Josephson junctions have also been fabricated using artificial superlattice films with as few as six superconducting copper-oxygen planes. Extrinsic and intrinsic d-wave effects in these junctions are discussed within the framework of novel designs for pi-circuitry and qubits. (C) 2004 American Institute of Physics.