Correction factor for determining the London penetration depth fromstrip resonators

The strip resonator technique is a popular way to measure the temperature (T)-dependent London penetration depth λ_L(T) in superconducting thin films. The temperature dependence can provide fundamental information about the superconducting energy gap and hence insight into the pairing mechanism. Since λ _L(T) characterizes the film's response to a magnetic field near the surface, it qualifies the suitability of the superconducting film for microwave device applications. There has been much controversy regarding the actual form of the temperature dependency, with some researchers reporting a weak-coupled Bardeen-Cooper-Schriefer (BCS)-like behavior and others favoring a Gorter-Casimir type fit. This paper shows that the disagreement can be at least partially attributed to a temperature sensitive term traceable to stray susceptance coupled into the resonator. The effect is inherent to the technique, but a simple procedure to compensate for it can be used and is presented here as a correction factor (1+ξ)