The Surface Impedance of Superconducting Aluminium at 3 Gc/s

In an attempt to find anisotropy of the penetration depth in super-conducting aluminium, such as would confirm a non-local relation between field and current, high-frequency measurements have been made on single-crystal wires of different orientations. No strong evidence for anisotropy has appeared, and there is some evidence from the measurements of surface resistance that the crystals used may not have had the best orientations to reveal any effect. The behaviour of the surface resistance and reactance has been carefully studied very near the transition temperature, and the latter has been found to show a maximum just below T c . There is qualitative but not quantitative agreement with the predictions of theory.