Electrodynamics of Superconductors
We shall begin with the three basic facts concerning the electrodynamics of superconductors: (A) Persistent currents—Flow of currents in certain metals in the superconducting phase seemed to indicate that these metals behave like perfect conductors. (B) The Meissner effect—However, the expulsion of magnetic field from the bulk of superconductor clearly indicated that a superconductor is a good diamagnet. (C) Flux quantization—If a multiply connected superconductor, say, a ring, is in a magnetic field and later cooled below the transition temperature, the expelled flux trapped inside the hole does not have arbitrary values but assumes values which are multiples of a unit quantity. This phenomenon throws great light on the microscopic theory of superconductivity. Flux quantization has been anticipated by London and Onsager.
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