HIGHLY ANISOTROPIC SUPERCURRENT TRANSPORT IN YBA2CU3O7-DELTA BICRYSTAL JOSEPHSON-JUNCTIONS

We report tunneling measurements on a large number of bicrystal YBa2Cu 3O7-delta Josephson junctions. The orientations of the bicrystals rela tive to their boundary was varied over 80 degrees while the misorienta tion angle was kept fixed at 32 degrees. A strong anisotropy in the ch aracteristic voltage IcRn of the Josephson junctions in the a-b plane was observed. IcRn's varied from about 80 to 2300 mu V at 4 K. The the oretical analysis shows that this variation may be explained as a comb ined effect of the presence of nodes in the gap function, either a gen eralized s wave with eight nodes or a d(x2-y2) wave, and anisotropy of the tunneling matrix elements.