EFFECT OF DC ELECTRIC-FIELD ON THE EFFECTIVE MICROWAVE SURFACE IMPEDANCE OF YBA2CU3O7 SRTIO3/YBA2CU3O7 TRILAYERS/

We have studied the effect of a dc electric field on the effective mic rowave surface impedance of a thin film YBa2Cu3O7/SrTiO3/YBa2Cu3O7 (YB CO/STO/YBCO) trilayer by a dielectric resonator technique. At large dc electric fields ( > 10(5) V/cm), both the effective surface resistanc e and reactance of the sample decrease monotonically with increasing d c voltage applied to the to YBCO film, yielding at 25 K and 24.7 GHz \ deltaR(s)/deltaV(dc)\ approximately 0.25 muOMEGA/V and \deltaX(s)/delt aV(dc)\ approximately 1.8 muOMEGA/V, respectively. A two-fluid analysi s indicates that the changes in the surface impedance can be explained in terms of field induced changes in the superconducting carrier dens ity of the top YBCO film.