Appendix E Theory of Superconductivity

Abstract

This appendix summarizes some basic aspects of the theory of superconductivity, covering the classical London equations, the BCS theory of weakly coupled low -T c materials, the unconventional superconductivity of strongly coupled high -T c compounds with its electronic and magnetic origin, and contributes some aspects to the understanding of the behavior of type II superconductors. London EquationsIn the classical model of superconductivity, the London equations (London and London 1935 ) are equivalent to Ohm ' s law j = σ · E for a normal electric conductor. The fi rst of the London equations [Eq. (E.1) ] represents a conductor with R = 0, while the second [Eq. (E.2) ] is equivalent to the Meissner -Ochsenfeld effect (Figure E.1 ), and describes the decay of a magnetic fi eld within a thin surface layer characterized by the penetration depth, λ L . E J = ∂ ∂ ( ) t m 525 Theory of Superconductivity Classic and Advanced Ceramics: From Fundamentals to Applications. Robert B. Heimann