The phenomena of superconductivity with alternating currents of high frequency

Abstract

In a previous paper the authors described experiments on the resistance of lead to currents having the high frequency of 10 7 per second. In these experiments no evidence was found of an abrupt change of resistance corresponding to the phenomenon of superconductivity that appears with direct currents when the critical temperature of 7·2° K. is passed, and it was pointed out that the partial silvering of the vacuum flasks that contained the lead coil was a source of error. In a set of new experiments to be described below unsilvered flasks were used, but the same technique of measurement was adopted. It was found that there was an abrupt decrease of the high frequency resistance at a temperature which appeared to be slightly lower than that characteristic of the transition to superconductivity with direct currents. Experiments with tin instead of lead showed a similar result. The transition temperature was progressively lowered as the frequency was increased. The behaviour of tantalum was investigated also, and this metal, too, showed a depression of the critical temperature for high frequency currents.