Superconducting current-phase relation in Nb/Au/(001)YBa2Cu3Ox   heterojunctions
  We probe directly the superconducting current-phase relations (CPR) of Nb/Au/(001) YBa2Cu3Ox heterojunctions prepared in epitaxial c-axis oriented YBa2Cu3Ox (YBCO) thin films. The measurements are performed by a single-junction interference experiment. Atomic Force Microscope observations and estimations made from I-V characteristics confirm the c-axis current transport. No deviation of the current-phase relation from a sinusoidal shape has been found within the experimental accuracy. Possible reasons of the absence of the second harmonic in the CPR due to a second order tunneling are discussed. 
P.V.Komissinski, E.Il'ichev, G.A.Ovsyannikov, S.A.Kovtonyuk,   M.Grajcar, Z.Ivanov, Y .Tanaka, N.Yoshida, and S.Kashiwaya