APS News


Nuclear Superconductivity

The debate in October 1997 APS News between John Michael Williams and Stuart Pittel on "Nuclear Superconductivity" has lost sight completely of its basic physics and history. The term was first used by David Pines at the 1957 Rehovot Conference on Nuclear Structure to point out that the new BCS theory, which was at that time far from being accepted, might also apply to nuclei. It suggested that any weak attractive interaction will give rise to coherent many-body states for the particles near the Fermi surface and an energy gap in their excitation spectrum.

At the same 1957 conference Giulio Racah independently described the same physics for atoms and nuclei in group-theoretical language. The bottom line was clearly stated by John Bardeen at that time in explaining the difference between BCS and Bose condensation. Cooper pairs are not bosons; they are overlapping fermion pairs where the size of a given pair is much larger than the mean distance between pairs, and where the Pauli principle is crucial. I used these ideas of Bardeen and Racah in my quantum mechanics book to show the unity of physics between various fields, rather than nitpicking over minor differences, and attempted to urge others to follow the precedent set by David Pines in encouraging communications between different areas.

Harry J. Lipkin
Weizmann Institute of Science
Rehovot, Israel

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Editor: Barrett H. Ripin