Superconducting current-phase relation of Nb/Au/(001) YBaCuO heterojunctions

Abstract The superconducting current–phase relation (CPR) of Nb/Au/(0 0 1) YBa 2 Cu 3 O x (YBCO) heterojunctions, prepared on epitaxial c -axis oriented YBCO thin films, has been measured in a single-junction interferometer. For the first time, the second harmonic of the CPR of such junctions has been observed. The appearance of the second harmonic and the relative sign of the first and second harmonics of the CPR can be explained assuming, that the macroscopic pairing symmetry of our YBCO thin films is of the d+s type.