Determination of the penetration depth of type II superconducting films

The superconducting penetration depth λ(0) at T = 0 was determined for NbN films from the temperature dependence of the frequency of a tunnel-diode-driven resonant circuit whose inductive element was a thin film meander line of superconducting NbN. The BCS temperature dependence of the penetration depth λ(t) was assumed. Measurements were made on two stoichometric NbN films 310 nm and 465 nm thick and a nitrogen-deficient film 55 nm thick. The values of λ(0) obtained were 276, 280, and 175 nm respectively. These values are compared with other determinations of λ(0). This method provides a simple method of obtaining λ(0) for thin films where other techniques may not be practical.