Application of a cavity perturbation method to the measurement of the complex microwave impedance of thin super- or normal conducting films

(Received 9 July 1993, revised 3 January 1994, accepted 23 February 1994)

Abstract
We present the application of a cavity perturbation method on thin super- or normal conducting films. The sample is placed in the center of the cavity in the maximum of the electric field. We have calculated the complex microwave impedance of the films with a new approach from the measured data. The method allows to determine the complex impedance of films with arbitrary thickness. In particular, films with thickness d small compared to the skin depth or the London penetration depth can be measured. Therefore, the impedance of superconducting films can be measured both in the normal and superconducting state. The method is an important completion to the conventional measurements of the surface resistance which replace one of the cavity walls by the film. This arrangement is problematic for films with or because in this case the field transmits through the film out of the cavity.