Josephson effect in Nb/Au/YBCO heterojunctions

c-axis oriented and 11(degree) tilted YBa/sub 2/Cu/sub 3/O/sub x/ (YBCO) thin films were deposited on [110] NdGaO/sub 3/ and (7 10 2) NdGaO/sub 3/ substrates correspondingly. Nb/Au/YBCO heterojunctions were fabricated using photolithography and ion beam milling. I-V curves of the heterojunctions based on tilted YBCO films showed zero bias anomaly conductance peak and large excess current. We observed the second harmonic ((proportional to) sin 2(phi)) of superconducting current in Nb/Au/YBCO heterojunctions in c-axis oriented YBCO films, although sinusoidal superconducting current-phase relation has been measured for heterojunctions in tilted ones. The obtained results are explained by d+s symmetry of YBCO superconducting order parameter.