Abstract
A needle-like a-axis oriented grain is artificially grown in a c-axis oriented NdBa2Cu3O7-δ (NBCO) thin film. Its long direction is parallel to the [110] direction of a (001) MgO substrate on a small rectangular area damaged by a focused Ga ion beam. The transmission electron microscopy (TEM) lattice image shows an atomically flat grain boundary and the lattice configuration of the grains. The boundary junction of the needle-like grain shows no supercurrent at zero magnetic field. However, an RSJ-type I-V curve with the supercurrent is observed under finite magnetic field. In addition, Shapiro steps are observed under microwave 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 π-junction caused by the d-wave symmetry of high-T c oxide superconductors.
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