BCS theory

Physics. a general quantum theory of superconductivity that describes many properties of superconducting materials. Also called Bardeen-Cooper-Schrieffer theory.

[after U.S. physicists J. BARDEEN, Leon N. Cooper (born 1930), and John R. Schrieffer (born 1929)]

* * *

Comprehensive theory that explains the behaviour of superconducting materials.

It was developed in 1957 by John Bardeen, Leon Cooper, and J. Robert Schrieffer (b. 1931), whose surname initials provide its name. Cooper discovered that electrons in a superconductor are grouped in pairs (Cooper pairs) and that the motions of all the pairs within a single superconductor constitute a system that functions as a single entity. An electric voltage applied to the superconductor causes all Cooper pairs to move, forming an electric current. When the voltage is removed, the current continues to flow because the pairs encounter no opposition. See also superconductivity.

* * *

▪ physics

      in physics, a comprehensive theory developed in 1957 by the American physicists John Bardeen (Bardeen, John), Leon N. Cooper (Cooper, Leon N.), and John R. Schrieffer (Schrieffer, John Robert) (their surname initials providing the designation BCS) to explain the behaviour of superconducting materials. Superconductors abruptly lose all resistance to the flow of an electric current when they are cooled to temperatures near absolute zero.

      Cooper had discovered that electrons in a superconductor are grouped in pairs, now called Cooper pairs, and that the motions of all of the Cooper pairs within a single superconductor are correlated; they constitute a system that functions as a single entity. Application of an electrical voltage to the superconductor causes all Cooper pairs to move, constituting a current. When the voltage is removed, current continues to flow indefinitely because the pairs encounter no opposition. For the current to stop, all of the Cooper pairs would have to be halted at the same time, a very unlikely occurrence. As a superconductor is warmed, its Cooper pairs separate into individual electrons, and the material becomes normal, or nonsuperconducting.

      Many other aspects of the behaviour of superconductors are explained by the BCS theory. The theory supplies a means by which the energy required to separate the Cooper pairs into their individual electrons can be measured experimentally. The BCS theory also explains the isotope effect, in which the temperature at which superconductivity appears is reduced if heavier atoms of the elements making up the material are introduced.

* * *