OBSERVATION OF JOSEPHSON PAIR TUNNELING BETWEEN A HIGH-TC CUPRATE (YBA2CU3O7-DELTA) AND A CONVENTIONAL SUPERCONDUCTOR (PB)

Josephson tunneling currents have been observed on low leakage Pb/insu lator/Y1-xPrxBa2Cu3O7-delta tunnel junctions. The junctions are planar with tunneling into the c axis. We have studied these Josephson curre nts on junctions with resistances varying by more than 2 orders of mag nitude. From the magnetic field modulation of the Josephson current, t he low temperature value and the temperature dependence from 1.3 to 4. 2 K of the c-axis penetration depth were measured. This observation of Josephson coupling along the c axis between a conventional supercondu ctor (Pb) and a cuprate raises questions about the proposed d-wave nat ure of the superconducting order parameter in the cuprates.