Superconducting surface resistance of thin amorphous Ga films on metallic substrates

The surface resistance of a metal coated with amorphous superconducting films is investigated. With an improved microwave cryostat and a two layer model considering the influence of the substrate, much thinner films can be used than previously. As an example the surface resistance of amorphous Ga is determined. A set of parameters₀/k_BT_c=2,27;_L=13,4 nm;₀=223 nm andl=1,0 nm describes the temperature dependence independent of thickness. As expected a model of free electrons is in agreement with the experimental results. For crystalline-Ga₀/k_BT_c=1,91;_L=24 nm;₀=163 nm and a much larger mean free pathl=22 nm is found.