Mechanism of Superconductivity

Abstract

IT was often assumed that the transition from normal conductivity to superconductivity may be connected with a kind of ‘spontaneous coupling’ of the conduction electrons. Some authors were even inclined to identify this phenomenon with ferromagnetism. Although this extreme point of view seems to be very improbable, some analogies with ferromagnetism must surely appear if any kind of ‘spontaneous coupling’ between electrons is responsible for superconductivity. For example, in this case the shape of the specific heat curve near the transition temperature must be analogous to that of ferromagnetic substances in the vicinity of the Curie point. W. Keesom and J. H. van den Ende,¹ and F. Simon and K. Mendelssohn² attempted to discover this anomaly of the specific heat in lead near the transition temperature (7.2° K), but they could not detect any trace of the effect. This result may be interpreted in two ways: either the hypothesis of the ‘spontaneous coupling’ of the conduction electrons in superconductors is completely wrong, or the number of the electrons which are concerned in conductivity is here so small in comparison with the number of atoms that the specific heat anomaly of the conduction electrons cannot be detected with calorimetric methods.