On the nature of the electric-field effect on YBa2Cu3O7-delta grain boundary junctions employing epitaxial SrTiO3 gate insulators

We have fabricated Josephson field-effect transistors based on YBa2Cu3O7-de lta bicrystal grain-boundary junctions (GBJs) and epitaxial SrTiO3 films as gate insulators. The SrTiO3 gate insulator shows high products of the brea kdown field E-bd and the dielectric constant epsilon(r) up to E(br)epsilon( r) = 1.3 X 10(10) V/m allowing measurements over a wide range of applied ga te electric-field E-g. The critical current I-c of the GBJs is found to dep end highly nonlinear on E-g. Remarkably, the measured I-c(E-g) are very sim ilar to the epsilon(r)(E-g) curves. This strongly suggests that the observe d electric-field effect is not due to a field-induced change in carrier con centration but is related to the dielectric properties of the SrTiO3 gate i nsulator. (C) 1999 American Institute of Physics. [S0003-6951(99)01907-5].