ABSTRACT
The most spectacular performance of which many-particle systems are capable is superconductivity: the ability of many metals to conduct an electric current without any resistance when they are cooled below a characteristic temperature. Both the experimental development of the many fascinating aspects of superconductivity, and the successful microscopic theory of the effect by Bardeen, Cooper and Schrieffer, constitute undoubtedly one of the really great triumphs of twentieth century physics. The chapter shows the close analogy between superconductivity and superfluidity, between electric supercurrents in Lead and macroscopic superflow in Helium, between the Meissner effect and the reduction of the moment of inertia. The superfluidity of the electrons in metals has its most drastic manifestations because of their electromagnetic properties. The modes which exist, longitudinal phonons and plasma oscillations, have nothing to do with superconductivity. Things would be different in a "neutral superconductor," that is in a condensed system of electrically neutral Fermions.
