@article{oai:niigata-u.repo.nii.ac.jp:00002114, author = {Yamada, Takemi and Ishizuka, Jun and Ono, Yoshiaki}, issue = {4}, journal = {Journal of the Physical Society of Japan, Journal of the Physical Society of Japan}, month = {Mar}, note = {We investigate a two-orbital model for iron-based superconductors to elucidate the effect of interplay between electron correlation and Jahn-Teller electron-phonon coupling by using the dynamical mean-field theory combined with the exact diagonalization method. When the intra- and inter-orbital Coulomb interactions, U and U′, increase with U = U′, both the local spin and orbital susceptibilities, χ_s and χ_o, increase with χ_s = χ_o in the absence of the Hund’s rule coupling J and the electron-phonon coupling g. In the presence of J and g, there are distinct two regimes: for J >__~ 2g^2 /ω_0 with the phonon frequency ω_0, χ_s is enhanced relative to χ_o and shows a divergence at J = J_c above which the system becomes Mott insulator, while for J <__~ 2g^2/ω_0, χ_o is enhanced relative to χ_s and shows a divergence at g = g_c above which the system becomes bipolaronic insulator. In the former regime, the superconductivity is mediated by antiferromagnetic fluctuations enhanced due to Fermi-surface nesting and is found to be largely dependent on carrier doping. On the other hand, in the latter regime, the superconductivity is mediated by ferro-orbital fluctuations and is observed for wide doping region including heavily doped case without the Fermi-surface nesting.}, pages = {044711-1--044711-8}, title = {Metal-insulator Transition and Superconductivity in the Two-orbital Hubbard-Holstein Model for Iron-based Superconductors}, volume = {83}, year = {2014} }