The surface impedance of normal and superconducting indium at 3000 Mc/s

Measurements have been made of the surface resistance and reactance of cylindrical single crystals of normal and superconducting indium at a frequency of about 3000 Mc/s. The absolute value of λ0, the penetration depth at 0 °K, is found to be (4.3 ± 0.2) x 10-6 cm, in good agreement with the prediction of the theory of Bardeen, Cooper & Schrieffer, and the temperature variation also agrees rather well, but not perfectly. Only slight evidence is found for the non-tensorial anisotropy of λ0 expected on the basis of Pippard’s non-local theory, and it is argued that the shortness of the coherence length reduces the magnitude of non-tensorial effects. The temperature variation of the superconducting resistance is found to be similar to that observed by Pippard in tin at 9400 Mc/s. The data provide evidence for the similarity in the high-frequency behaviour of superconductors suggested by Faber & Pippard. As expected, the surface resistance and reactance in the normal state show marked nontensorial anisotropy. From the resistance the area of the Fermi surface in indium is estimated to be 0.93 of the area of a free electron sphere holding 3 electrons per atom.