MODELING OF THE MICROWAVE SURFACE IMPEDANCE OF CURRENT BIASED YBA2CU3O7-DELTA THIN-FILMS

A theoretical and experimental investigation is made of the surface im pedance of dc current biased high-quality epitaxial YBa2Cu3O7-delta th in films using a coplanar resonator technique. The isotropic Ginzburg- Landau theory and a current-dependent coupled-grain model are used to model the resonant frequency shift and the change in unloaded quality factor Q(0) due to the bias current. Good quantitative agreement is ob tained between the two models and the measured resonant frequency shif t. The change in eo, determined from measurements, can be explained by the coupled-grain model. The Ginzburg-Landau theory predicts a change in Q(0) which is several times less than given by measurements. (C) 1 997 American Institute of Physics.