Superconductivity

Abstract

Superconductivity derives from a kind of two-electron bound state called the Cooper pair. Many Cooper pairs are multiply overlapping with one another, in contrast with an ordinary bound state such as hydrogen molecule. Then at any spatial point one cannot pinpoint a pair. This feature is related to the tiny binding energy as compared with the Fermi energy. This chapter explains basic mechanisms leading to formation of the Cooper pair. The discussion includes some recent development, concerning new types of superconductors with high transition temperatures.