Advances in high Tc grain boundaryjunctions

We review results on two novel types of grain-boundary Josephson junctions in the high-criticaltemperature cuprate superconductors. The quality of YBa2Cu3O72d biepitaxial grainboundary 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 p-circuitry and qubits.