Surface impedance of a superconductor having a film of ordinary metal on its surface

The mechanism for the losses brought about by a thin layer of ordinary metal on the surface of a superconductor is considered. It is noted that in the manufacture of various superconducting microwave systems a thin layer (tens to thousands of A thick) of nonsuperconducting metal can form on the surface and greatly increase losses in the resonance system. The impedance arising from the metal is calculated, and it is noted that the layer may also explain the residual resistance of superconducting systems operating in the microwave region.