The Nature of the Superconducting State

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Abstract
It is tentatively suggested that the superconducting state of metallic electrons may arise by application of perturbation theory to Bloch's theory. The excited states of a metal, on the usual theory, form a continuum whose lower boundary is the normal state. It is shown that under some circumstances there are nondiagonal matrix components of energy between states of this continuum, which would tend to depress a few of the lowest states below their normal positions. These special states of the metal would resemble a thermodynamic phase, stable only at the lowest temperatures, and having practically zero entropy, in agreement with present theories of the thermodynamics of superconductivity. They would also tend to have extremely low resistance, on account of the small concentration of energy levels per unit energy range. It is therefore suggested that these states may constitute the superconducting state. It is shown that superconductivity is not to be expected for the alkalies, or for Cu, Ag or Au; and that it is to be expected only at extremely small temperatures for transition metals, as W, Fe, Ni, Pt; thereby accounting for most of the metals which are known not to be superconducting at temperatures so far attained.

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