Detailed measurements of Josephson tunneling between ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathit{y}}$ (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.

• Received 22 December 1993

DOI:https://doi.org/10.1103/PhysRevB.49.12388