ELECTRIC-FIELD EFFECT ON ULTRATHIN YBA2CU3O7-DELTA GRAIN-BOUNDARY JOSEPHSON-JUNCTIONS

The effect of electric field on ultrathin YBa2Cu3O7-delta grain bounda ry Josephson junctions has been investigated. A conventional metal ins ulator superconductor field effect transistor structure consisting of a Pr0.55Y0.45Ba2Cu3O7-delta/YBa2Cu3O7-delta bilayer channel, a crystal line SrTiO3 dielectric, and an Au gate electrode is deposited on a SrT iO3 bicrystal substrate. At high bias current (I(bias)much greater tha n I-c) the observed effect is compatible with a parallel resistor mode l using a value close to the bulk charge carrier density of YBa2Cu3O7- delta. At low bias current (I(bias)greater than or equal to I-c) an en hanced field effect not compatible with a parallel resistor model is o bserved. This enhanced effect is related to the field dependent dielec tric properties of the crystalline SrTiO3 insulation layer. (C) 1995 A merican Institute of Physics.