Effective and intrinsic surface impedances of high-T/sub c/ superconducting thin films

The microwave effective surface impedances of different stacks made of YBa/sub 2/Cu/sub 3/O/sub 7/ films, dielectric materials, and bulk normal metals were computed, using the two-fluid model of superconductors and conventional transmission line theory. these effective impedances are compared to the calculated intrinsic surface impedances of the stacked superconducting films with a penetration depth of 220 nm and a normal resistivity of 100 mu Omega -cm at 77 K. The films were assumed to be epitaxial, with thicknesses ranging from a few nanometers to 1 mu m. The discrepancy between the effective surface resistances or reactances and the corresponding intrinsic values, determined at 10 GHz, exhibits a sharp peak at resonance. The effective surface reactance also shows huge variations around the resonance conditions and may be negative. Moreover, geometries resulting in an effective resistance smaller than the film intrinsic value have been found.<
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