ELECTRIC-FIELD EFFECTS ON YBA2CU3O7-DELTA GRAIN-BOUNDARY JOSEPHSON-JUNCTIONS

Various effects of the electric field on YBa2Cu3O7-delta grain boundar y Josephson junctions were studied using inverted metal-insulator-supe rconductor (MIS) samples which employed bicrystal SrTiO3 substrates as insulators. The critical currents, I(c) of the junctions were regulat ed by gate voltages with the field-induced changes in charge carrier d ensities. Furthermore, a significant field eff ect on equidistant step structures observed in I-V curves was found. The equidistant steps ca n be ascribed to self-resonances of the ac Josephson current in the gr ain boundary junctions. The gate voltages shifted the step voltages co rresponding to resonance frequencies of the grain boundary toward high voltages. This appears to be a consequence of the field dependence of dielectric properties of grain boundary junctions.