In the field of superconductivity, Anderson's theorem states that superconductivity in a
conventional superconductor
Conventional superconductors are materials that display superconductivity as described by BCS theory or its extensions. This is in contrast to unconventional superconductors, which do not. Conventional superconductors can be either type-I or typ ...
is robust with respect to (non-magnetic) disorder in the host material. It is named after
P. W. Anderson, who discussed this phenomenon in 1959, briefly after
BCS theory
In physics, the Bardeen–Cooper–Schrieffer (BCS) theory (named after John Bardeen, Leon Cooper, and John Robert Schrieffer) is the first microscopic theory of superconductivity since Heike Kamerlingh Onnes's 1911 discovery. The theory descr ...
was introduced.
One consequence of Anderson's theorem is that the critical temperature ''T''
c of a conventional superconductor barely depends on material purity, or more generally on defects. This concept breaks down in the case of very strong disorder, e.g. close to a
superconductor-insulator transition. Also, it does not apply to
unconventional superconductor
Unconventional superconductors are materials that display superconductivity which is not explained by the usual BCS theory or its extension, the Eliashberg theory. The pairing in unconventional superconductors may originate from some other mecha ...
s. In fact, strong suppression of ''T''
c with increasing defect scattering, thus non-validity of Anderson's theorem, is taken as a strong indication for superconductivity being unconventional.
References
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Superconductivity