Angle-resolved Andreev bound states in anisotropic d-wave high-$T_c$ ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{7-y}$ superconductors

An unusual technique utilizing the two-dimensional junction configuration is introduced to study the pairing symmetry of a ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{7-y}$ cuprate superconductor. The zero bias conductance peak due to the Andreev bound states was measured for the ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{7-y}/\mathrm{I}/\mathrm{A}\mathrm{g}$ ramp-edge tunnel junctions with different crystal-interface boundary angles fabricated on the same chip. It was found to develop monotonically as the angle was increased and became a maximum at 45°. Two gaplike structures were also found at the intermediate angle of 30°. The result implies that $d_{x2\mathrm{}-y2\mathrm{}}$-wave pairing symmetry predominates in this cuprate.