ABSTRACT
The first great difficulty in the development of the theory was to discover the nature of the interaction responsible for the transition to superconductivity. The isotope effect makes it clear that the ions in the metal play an essential role in superconductivity. The bcs theory gives a complete account of superconductivity, and it would take a great deal of space to go into all its implications. Equation for the binding energy of a Cooper pair is of the right magnitude for a theory of superconductivity. Superconductivity disappears when the difference in energy between up spin and down spin states at the Fermi surface exceeds the binding energy of the Cooper pair. G. M. Eliashberg’s formulation is the natural starting point for the theory of strong-coupling superconductors, in which the electron-phonon interaction is too strong to be treated in perturbation theory. The simplest consequence of strong electron-phonon coupling is that the room-temperature resistivity is high, since it is determined by electron-phonon scattering.
