EXPERIMENTAL-EVIDENCE FOR A D-WAVE PAIRING STATE IN YBA2CU3O7-Y FROM A STUDY OF YBA2CU3O7-Y/INSULATOR/PB JOSEPHSON TUNNEL-JUNCTIONS

Detailed measurements of Josephson tunneling between YBa2Cu3O7-, (YBCO) and Pb using YBCO/[MgO (or native barrier)]/Pb junctions with YBCO films either c-axis or a-axis oriented are presented. In the case of the c-axis-oriented films, the dependence of the Josephson critical current on the applied magnetic field exhibits diffraction patterns close to that characteristic of a d-wave superconductor. The temperature dependence of the Josephson critical current also shows an anomalous behavior. Incidentally, the diffraction pattern exhibits less-sensitive behavior to magnetic fields at low temperatures. These results suggest the possibility of d-wave symmetry for a YBCO superconductor.