Highly anisotropic supercurrent transport in YBa2Cu3O7-δ bicrystal Josephson junctions

We report tunneling measurements on a large number of bicrystal YBa2Cu3O7-delta Josephson junctions. The orientations of the bicrystals relative to their boundary was varied over 80 degrees while the misorientation angle was kept fixed at 32 degrees. A strong anisotropy in the characteristic 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 theoretical analysis shows that this variation may be explained as a combined effect of the presence of nodes in the gap function, either a generalized s wave with eight nodes or a d(x2-y2) wave, and anisotropy of the tunneling matrix elements.