MACROSCOPIC QUANTUM EFFECTS IN SUPERFLUIDS

A general account of macroscopic quantum effects in superfluid systems is given, covering both superfluid helium and superconductors. An elementary theory of superflow is first developed based on the idea of the condensate wave function, this function being introduced as an essentially phenomenological concept. It is shown how this theory leads to the prediction of the quantization of circulation, of the quantization of flux and of related effects, and how it contains within it the idea, originally proposed by F. London, that a superfluid system exhibits long-range order in the momentum vector. The experimental evidence that the theory is correct is reviewed and the link with microscopic theory is made. The first part of the article is intended to be quite elementary and self-contained; the more sophisticated theory is confined to the last section.