title: Orbital-fluctuation-mediated superconductivity in iron pnictides: analysis of the five-orbital Hubbard-Holstein model.
abstract: In iron pnictides, we find that the moderate electron-phonon interaction due to the Fe-ion oscillation can induce the critical d-orbital fluctuations, without being prohibited by the Coulomb interaction. These fluctuations give rise to the strong pairing interaction for the s-wave superconducting (SC) state without sign reversal (s(++)-wave state), which is consistent with experimentally observed robustness of superconductivity against impurities. When the magnetic fluctuations due to Coulomb interaction are also strong, the SC state shows a smooth crossover from the s-wave state with sign reversal (s(+/-)-wave state) to the s(++)-wave state as impurity concentration increases.
authors.affiliation: Department of Physics, Nagoya University and JST, TRIP, Furo-cho, Nagoya 464-8602, Japan.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Kontani
authors.forename: Seiichiro
authors.initials: S
authors.lastname: Onari