Field effects on the dielectric property of YBCO bicrystal grain boundary junctions

Electric field effects on YBCO grain boundary Josephson junctions combined with inverted MIS (Metal, Insulator, Superconductor) structures were studied. Current steps and hysteresis recognized in current-voltage curves were strongly affected by the field. The current steps were attributed to the self-excited resonances, i.e., Fiske steps. Both the effects were interpreted by the field dependence of the effective dielectric constant of the grain boundary which has a certain contribution from the large dielectric constant of SrTiO/sub 3/ substrates. The effective dielectric constant normalized with barrier thickness of the junction was estimated to be about 40 nm/sup -1/ for the zero gate voltage and was decreased by a factor of 2 with the electric field of /spl plusmn/16 kV/cm. This feature is assumed adequate for tuning the phase velocity in the bicrystal grain boundaries.<>