Advances in YBa2Cu3O7−δ Grain Boundary Biepitaxial Josephson Junctions: Transport Properties and Mesoscopic Effects

We report on the latest developments in the study of transport properties of YBa₂Cu₃O_7-delta (YBCO)-based grain boundary (GB) biepitaxial Josephson junctions. We have successfully extended the fabrication process, originally developed for (110) oriented SrTiO₃ substrates, to (110) oriented LaAlO₃ substrates in view of microwave applications. We will report, also, on the observation of conductance fluctuations, we believe related to the coherent diffusion of quasi-particles across the GB. These results, together with the recent observation of macroscopic quantum tunneling and energy level quantization in these junctions, could help cast some light on the mechanism involved in transport across grain boundaries and in revising the role and the effect of quasi particles in d-wave transport.