ABSTRACT
This chapter reviews the state of our knowledge of superconductivity, both experimental and theoretical, as it was in 1957 when the microscopic theory was formulated by Bardeen, Cooper, and Schrieffer, which is now known universally as the BCS theory. It deals with an account of the fundamental properties which distinguishes a superconductor from other solids and of its behavior in mechanical, thermal, and electromagnetic fields. It also discusses the thermodynamics of superconductors and the several phenomenological theories that are proposed to explain these properties. The BCS theory gives its own fundamental criterion for the occurrence of superconductivity in terms of the interactions of the elementary excitations in a solid. Landau gave in 1937 a phenomenological theory of second-order transitions, introducing the important concept of an order parameter. One other point about the jump in the specific heat is that its magnitude is thermodynamically related to the temperature dependence of the critical field, and this has been experimentally verified.
