Theories of Superconducting Transitions

Abstract

Nearly free independent electrons in metals become correlated on lowering temperatures, causing a superconducting transition. Observed anomalies at the transition threshold are informative about the correlations, but not quite revealing. On the other hand, the critical temperature Tc varies with isotopic mass M composing the lattice, providing evidence for the lattice to be involved in the superconducting mechanism. Nevertheless, electron–electron correlations are essential in such a multielectron system in a superconducting crystal. Following Fröhlich’s proposal for electron–phonon interactions, Cooper proposed an electron-pair model for superconducting charge carriers. Based on this model, Bardeen, Cooper, and Schrieffer presented the theory of superconducting transitions, which is the objective for discussions in this chapter. The superconducting transition can thereby be described in terms of electron-pair carriers, in analogy of pseudospin clusters for structural phase changes.