Superconducting pairing symmetry in YBa2Cu3O7-x from a study of Josephson tunnel junctions

The biepitaxial YBa2Cu3O7-x(YBCO)/CeO2/MgO Josephson junctions and c-axis Y BCO/Au/Pb junctions have been fabricated to investigate the pairing state i n YBCO. As a result, for the in-plane biepitaxial YBCO grain boundary junct ions, both the integral and half-integral Shapiro steps are observed under zero applied magnetic field, suggesting the possibility of d-wave pairing i n YBCO. On the other hand, Josephson tunneling currents have been observed on the YBCO/Au/Pb junctions with tunneling along the c axis of the YBCO fil ms. The dependence of the Josephson critical current on the applied field f or the YBCO/Au/Pb junctions exhibits an unconventional diffraction pattern which is close to the characteristic of a predominantly d-wave superconduct or. The results are discussed in terms of the existing s-wave and d-wave sy mmetry theories.