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BCS theory of superconductivity (Read 1932 times)
Gerrit-Jan Linker
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BCS theory of superconductivity
13.10.12 at 22:15:59
 
BCS theory of superconductivity
 
BCS theory, proposed by John Bardeen, Leon Neil Cooper, and John Robert Schrieffer (BCS) in 1957, is the first microscopic theory of superconductivity since its discovery in 1911. The theory describes superconductivity as a microscopic effect caused by a condensation of Cooper pairs into a boson-like state.
 
The picture is the following:
An electron moving through a conductor will attract nearby positive charges in the lattice. This deformation of the lattice causes another electron, with opposite spin, to move into the region of higher positive charge density. The two electrons then become correlated. Because there are a lot of such electron pairs in a superconductor, these pairs overlap very strongly and form a highly collective condensate. In this "condensed" state, the breaking of one pair will change the energy of the entire condensate - not just a single electron, or a single pair. Thus, the energy required to break any single pair is related to the energy required to break all of the pairs (or more than just two electrons). Because the pairing increases this energy barrier, kicks from oscillating atoms in the conductor (which are small at sufficiently low temperatures) are not enough to affect the condensate as a whole, or any individual "member pair" within the condensate. Thus the electrons stay paired together and resist all kicks, and the electron flow as a whole (the current through the superconductor) will not experience resistance. Thus, the collective behavior of the condensate is a crucial ingredient necessary for superconductivity.
 
Source:
http://en.wikipedia.org/wiki/BCS_theory
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« Last Edit: 13.10.12 at 22:17:50 by Gerrit-Jan Linker »  

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