title: Violation of Anderson's theorem for the sign-reversing s-wave state of iron-pnictide superconductors.
abstract: 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, contrary to the prediction based on simple orbital-less models. The present study provides a stringent constraint on the pairing symmetry and the electronic states in iron pnictides.
authors.affiliation: Department of Applied Physics, Nagoya University and JST, TRIP, Furo-cho, Nagoya 464-8602, Japan.
authors.forename: Seiichiro
authors.initials: S
authors.lastname: Onari
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Kontani