Highly anisotropic supercurrent transport inYBa2Cu3O7−δbicrystal Josephson junctions

We report tunneling measurements on a large number of bicrystal ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{7-\delta }$ Josephson junctions. The orientations of the bicrystals relative to their boundary was varied over $80°$ while the misorientation angle was kept fixed at $32°$. A strong anisotropy in the characteristic voltage $I_c{R}_n$ of the Josephson junctions in the $a-b$ plane was observed. $I_c{R}_n$’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 $d_{x^2-y^2}$ wave, and anisotropy of the tunneling matrix elements.