POINT-CONTACT CHARACTERISTICS OF HIGH-ANGLE YBA2CU3O7-DELTA STEP-EDGE JUNCTIONS

Point-contact characteristics with pronounced subgap structures and excess current at high voltages have been observed for YBa2Cu3O7-delta grain-boundary junctions across high-angle (alpha > 65 degrees) substrate steps. The measured current-voltage characteristics could be described in terms of the Octavio, Tinkham, Blender, and Klapwijk model by taking into account inelastic scattering. A large gap voltage, Delta(4.2 K) = 30-33 meV, could be extracted from the characteristics, which indicates that the small characteristic voltage I(c)R(n) much less than Delta/e of grain-boundary junctions might be associated with the boundary itself, rather than with a reduction of the energy gap near the boundary.