Observation of quasiparticle Andreev bound states using YBa2Cu3O7-y/Ag ramp-edge junctions with different interface geometries

We present measurements on quasiparticle tunneling using YBa2Cu3O7 - y, (YB CO)/Ag ramp-edge junctions. The tunnel direction was toward the CuO2 planes . Two junctions with different tilted angles between the a axis of YBCO and the junction boundary were fabricated on the same substrate simultaneously . For the junctions with the tilted angle of 45 degrees, the zero-bias cond uctance peak (ZBCP) was observed. On the contrary, for those fabricated wit h the tilted angle of 0 degrees, a dip structure around zero bias was mostl y observed. The results are consistent with the recent studies on the Andre ev reflection between a d(x2 - y2)-wave superconductor and a normal metal. The dependencies of ZBCP on temperature and magnetic field are also present ed. [S0163-1829(99)01130-3].