The penetration depth in impure superconducting tin

Abstract

A new method is described for measuring the surface impedance of metals at low temperatures and at radio-frequencies. Using this method, the surface impedance of normal tin and the penetration depth λ in superconducting tin have been studied at about 9 Mc/s frequency as a function of impurity content. The measured surface impedances agree well with the values expected, and the penetration depths increase with impurity content, in confirmation of Pippard's observations (14) at 9400 Mc/s. The variation of λ with reduced temperature t is well represented by the equation λ/λ₀ = (1 − t⁴)^−½, in impure as well as in pure tin. The absolute value of λ found for pure tin is about 4 × 10⁻⁶ cm., significantly lower than the values previously found.