FABRICATION OF NDBA2CU3O7-DELTA(110)-(001) GRAIN-BOUNDARY JOSEPHSON-JUNCTION BY FOCUSED ION-BEAM METHOD

A needle-like a-axis oriented grain is artificially grown in a c-axis oriented NdBa2Cu3O7-delta (NBCO) thin film. Its long direction is para llel to the [110] direction of a (001) MgO substrate on a small rectan gular area damaged by a focused Ga ion beam. The transmission electron microscopy (TEM) lattice image shows an atomically flat grain boundar y and the lattice configuration of the grains. The boundary junction o f the needlelike grain shows no supercurrent at zero magnetic held. Ho wever, an RSJ-type I-V curve with the supercurrent is observed under f inite magnetic held. In addition, Shapiro steps are observed under mic rowave irradiation, indicating that the junction works as a Josephson junction. This supercurrent suppression at zero field can be explained by taking the junction to be a pi-junction caused by the d-wave symme try of high-T-c oxide superconductors.