Violation of Anderson's theorem for the sign-reversing s-wave state of iron-pnictide superconductors.

@article{Onari2009ViolationOA,
  title={Violation of Anderson's theorem for the sign-reversing s-wave state of iron-pnictide superconductors.},
  author={Seiichiro Onari and Hiroshi Kontani},
  journal={Physical review letters},
  year={2009},
  volume={103 17},
  pages={177001}
}
Based on the five-orbital model, we study the effect of local impurity in iron pnictides, and find that the interband impurity scattering is promoted by the d-orbital degree of freedom. This fact means that the fully gapped sign-reversing s-wave state, which is predicted by spin fluctuation theories, is very fragile against impurities. In the BCS theory, only 1% impurities with intermediate strength induce huge pair breaking, resulting in the large in-gap state and prominent reduction in Tc… CONTINUE READING