An experiment on the mechanism of superconductivity

The Thomson coefficient of superconductive lead has been determined by a direct experiment and found to be zero (<4x 10-9 V/deg.). It has been concluded from this result that the electrons engaged in a superconductive current remain energetically at absolute zero. The apparent electronic specific heat of a superconductor is assumed to be due to an excitation of electrons from the lowest state. The magnetic data suggest that this apparent specific heat is proportional toT 3 . A purely empirical model of the electronic term system for a superconductor has been suggested in which a small energy gap ( ~10-4 eV) separates the upper limit of the Fermi distribution at absolute zero from a continuum of higher states. The frictionless transport of electrons is supposed to be due to metastable states within the gap in which energy cannot be dissipated. In such a model the number of superconductive electrons at absolute zero has been calculated to be of the order of 10-3 of the number of atoms. Attention has been drawn to a peculiar similarity between the frictionless transport in superconductors and that in liquid helium II. It has been concluded that the cause for both phenomena may be essentially the same—an aggregation of freely mobile particles of zero thermal energy which follows similar rules irrespective of the nature of the particles involved.