Anderson's theorem (superconductivity)

In the field of superconductivity, Anderson's theorem states that superconductivity in a conventional superconductor 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 was introduced.^[1]

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 superconductors. 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.^[2]