OBSERVATION OF BOUNDARY JOSEPHSON-JUNCTION WITH D-WAVE PAIRING CHARACTERISTICS

Josephson junctions have been fabricated along boundaries between (001) of a-axis oriented YBCO grains and (110) of c-axis oriented YBCO grains. These grain boundaries are formed along an a-axis oriented grain surrounding by the YBCO c-axis oriented film deposited on a MgO (001) substrate. TEM observation shows clear lattice image of the grain boundary. A typical RSJ type I-V curve with J(c) of 1.4 x 10(4) A/cm(2) at 4.2 K. and Shapiro steps under microwave irradiation are observed, indicating that the boundary works as a Josephson junction. The diffraction pattern of I-c under magnetic field has the minimum value at zero magnetic field. This property is analogous to one expected for a s-wave-d-wave junction.