Josephson effects in YBa2Cu3Oy grain boundary junctions on (100)MgO bicrystal substrates

The grain boundary YBa₂Cu₃O_y(YBCO) Josephson junctions are fabricated on (100)MgO bicrystal substrates with a misorientation angle of 24° and the microwave properties of Josephson effects are studied up to millimeter-wave range. Strong [100]//[010] and [010]//[100] in-plane orientations are observed at the junction interface of a YBCO film, whose microscopic geometries are discussed in connection with the observed Josephson effects. The directly observed maximum Josephson microwave self-radiation powers from the junction at receiver frequencies of f_REC=22 GHz and 47 GHz are 3.2×10^-12 W and 5.6×10^-14 W, respectively. The observed characteristic voltage (V_c) is 4.4 mV, corresponding to the frequency of about 2 THz at 4.2 K.