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Bardeen, John

metal theory electrons pair

[bah(r )deen ] (1908–91) US physicist: co-inventor of the transistor and contributor to the BCS theory of superconductivity.

Bardeen came from an academic family and studied electrical engineering at the University of Wisconsin. He worked as a geophysicist for 3 years at the Gulf Research Laboratories before obtaining a PhD in mathematical physics at Princeton under in 1936. Following periods at the University of Minnesota and the Naval Ordnance Laboratory, Bardeen joined a new solid-state physics group at Bell Telephone Laboratories at the end of the Second World War. His major creative work then began, and continued after his move from Bell to a professorship at the University of Illinois in 1951. Bardeen together with and received the Nobel Prize for physics in 1956, for the development of the point-contact transistor (1947). He won the Nobel Prize again in 1972, shared with and , for the first satisfactory theory of superconductivity (1957), now called the BCS theory. Bardeen thereby became the first man to receive the Nobel prize for physics twice.

Superconductivity was discovered in 1911 by . A metal brought into this state by low temperature (<15 K) expels magnetic field and will maintain electric currents virtually indefinitely (it shows zero resistance). Work in 1950 had revealed that the critical temperature is inversely proportional to the atomic mass of the metal, and Bardeen inferred that the oscillations of the metal lattice must be interacting with the metal conduction electrons. Cooper (1956) at the University of Illinois showed that electrons can weakly attract one another by distorting the metal lattice around them, forming a bound pair of electrons (Cooper pair) at low temperature when thermal vibrations are much reduced. Bardeen, Cooper and Schrieffer then assumed that a co-operative state of many pairs formed and that these pairs carried the super-conducting current. The members of a pair have a common momentum and the scattering of one electron by a lattice atom does not change the total momentum of the pair, so that the flow of electrons continues indefinitely.

The BCS theory not only greatly revived interest in superconductivity but showed how quantum theory can give rise to unusual phenomena even on a macroscopic scale.

Bardi, Giovanni dé [next] [back] Barbirolli, Sir John (actually, Giovanni Battista)

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