Nonsinusoidal current-phase relationship of grain boundary Josephson junctions in high-Tc superconductors

For various configurations of Josephson junctions incorporating superconductors with unconventional ;order parameter symmetry, such as most high-T-c cuprates, deviations from the standard sinusoidal current-phase dependence have been predicted. To this point, these deviations have never been observed experimentally. We have measured the current-phase relation of high-T-c Josephson junctions, namely, YBa2Cu3O7-x thin film bicrystals, comprising symmetric 45 degrees [001] tilt grain boundaries. The current-phase relations of all junctions investigated were found to be extremely nonharmonic, in agreement with a d(x)2(-y)2-wave dominated symmetry of the order parameter.