Superconductivity, I: Phenomenology

Abstract

Materials becoming superconductors as they are cooled below the critical temperature T_c are mentioned; the main properties of the superconducting state are briefly reviewed. The role of the magnetic field in squeezing a superconductor and increasing its energy is shown. London equation and its Pippard non-local generalization connecting the current density j(r) to the vector potential A(r) are presented; these phenomenological equations embody the basic superconducting properties. The Ginzurg-Landau theory, for type II superconductors, is also presented. We mentioned in Chap. 8, Sect. 8.5.2, that the main characteristics of the superconductive state of matter are the absence of magnetic field inside a superconductor (Meissner-Ochenfeld effect [22.1]; perfect diamagnetism) and the zero DC resistivity [22.2]. Superconductivity occurs for several elemental metals and many compounds below the critical temperature T_c, which depends on the material; superconductivity can be destroyed by the application of a sufficiently strong external magnetic field.