Angle-resolved Andreev bound states in anisotropic d-wave high-T-c, YBa2Cu3O7-y superconductors

An unusual technique utilizing the two-dimensional junction configuration i s introduced to study the pairing symmetry of a YBa2Cu3O7-y cuprate superco nductor. The zero bias conductance peak due to the Andreev bound states was measured for the YBa2Cu3O7-y/I/Ag ramp-edge tunnel junctions with differen t crystal-interface boundary angles fabricated on the same chip. It was fou nd to develop monotonically as the angle was increased and became a maximum at 45 degrees. Two gaplike structures were also found at the intermediate angle of 30 degrees. The result implies that d(x2-y2)-wave pairing symmetry predominates in this cuprate.