JOSEPHSON TUNNELING BETWEEN A CONVENTIONAL SUPERCONDUCTOR (PB) AND YBA2CU3O7-DELTA

The symmetry of the order parameter in the high T-c cuprates can be probed by investigation of its phase using various squid configurations. Even more simply, an investigation of the overlap of the pair wavefunction of a conventional superconductor with a high T-c cuprate should reveal the symmetry of the cuprate. We have been studying this overlap by Josephson tunneling (tunneling as opposed to SNS or weak link) between Pb and YBa(2)Cu(3)O(7-)delta. The observation of a Josephson coupling in the c-axis implies the order parameter in the cuprate is not strictly d(x)2-(y)2 symmetry. Measurements of the magnetic field dependence of the Josephson current I-c(B) allow a direct, d.c. measurement of the low temperature penetration depth. Studies have been performed on twinned and untwinned single crystals and thin films.