The superconducting penetration depth in thin films of lead

Abstract

We measured the attenuation of an axial magnetic field by cylindrical thin films of superconducting lead. We also measured the normal-state resistance of the same films. The magnetic field was measured by using a superconducting magnetometer. From the temperature dependence of the normalstate resistance, we determined the film thickness and the electron mean free path. From the field attenuation, the film thickness, and the mean free path, we derived the superconducting conductivity, the London penetration depth ~ and penetration depth A, which would be expected for pure, bulk lead. In order to interpret our field-attenuation measurements, we found it important to know the value of the electromagnetic coherence length as a function of temperature. To this end and to compare our experimental results with theory, we calculated the coherence length and the superconducting conductivity at finite temperatures by using the strong-coupling theory of superconducting lead. Our experimental results for the superconducting conductivity at zero temperature and its temperature dependence agree well with our own theoretical results and previous, zero-temperature, theoretical results. We find the bulk zero-temperature penetration depth A(O) should be 453 + 8 K.