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Surface properties are critical to the capabilities of superconductingmicrowave devices. The native oxide of niobium-based devices is thought toconsist of a thin normal conducting layer. To improve understanding on theimportance of this layer, an attempt was made to replace it with a more easilycontrolled gold film. A niobium sample host microwave cavity was used tomeasure the surface resistance in continuous wave operation at 4.0 GHz and 5.2GHz. Sample conditions studied include temperatures ranging from 1.6 K to 4.2 Kwith RF magnetic fields on the sample surface ranging from 1 mT to the maximumfield before the superconducting properties were lost (quench field). Thenominal film thickness of the gold layer was increased from 0.1 nm to 2.0 nm infive steps to study the impact of the normal layer thickness on surfaceresistance on a single niobium substrate. The 0.1 nm film was found to reducethe surface resistance of the sample and to enhance the quench field. With theexception of the final step from a 1.5 nm gold film to 2.0 nm, the magnitude ofthe surface resistance increased substantially with gold film thickness. Thenature of the surface resistance field-dependence appeared to be roughlyindependent from the gold layer thickness. This initial study provides newperspectives and suggests avenues for optimizing and designing surfaces forresonant cavities in particle accelerators and quantum informationapplications.

Measurements of the amplitude-dependent microwave surface resistance of an Au/Nb bilayer