ABSTRACT
Superconductivity arises from a very complicated set of interactions between the electrons in a metal. This chapter considers a very simplified model of the interaction of a pair of electrons in a metal, it is an instructive example of how quantum mechanics works and the main features of this model are at the starting point of the modern theory of superconductivity. In a metal one has a repulsive Coulomb interaction between the electrons, together with an attractive interaction between the electrons and ions. The total interaction between any two electrons is a composite of this attraction plus the Coulomb repulsion. In some metals, this total interaction is attractive for electrons near the Fermi surface.
