NONSINUSOIDAL CURRENT-PHASE RELATIONSHIP OF GRAIN-BOUNDARY JOSEPHSON-JUNCTIONS IN HIGH-T-C SUPERCONDUCTORS

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