Frequency Dependence of the Skin Depth in Superconducting Tin

Abstract

The first measurements of the frequency dependence of the real part of the superconducting skin depth δ_r(v, t), in polycrystalline tin films, are reported using a new technique of measurement. The technique is similar to the usual cavity technique, except that the cavity in question is a rectangular Sn–SnO_x–Sn Josephson tunnel junction. The cavity is self‐excited via the ac Josephson effect; the resonant frequencies of the cavity are measured from which δ_r(v, t) is deduced. The measurements extend from 0≤v≤220 GHz and 0.5≤t≤0.952. The results are compared with Miller's calculations of δ_r for Sn, which are based on the Mattis‐Bardeen theory and are found to be in agreement for t≤0.800. Above this temperature only qualitative agreement exists because the assumptions under which the calculations were made are here only partly satisfied.