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Metal-insulator Transition and Superconductivity in the Two-orbital Hubbard-Holstein Model for Iron-based Superconductors
Metal-insulator Transition and Superconductivity in the Two-orbital Hubbard-Holstein Model for Iron-based Superconductors
Yamada, Takemi
7096
Ishizuka, Jun
7097
Ono, Yoshiaki
62
iron pnictide superconductor
multi-orbital system
Jahn-Teller electron-phonon coupling
orbital fluctuation
magnetic fluctuation
dynamical mean-field theory
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.
journal article
The Physical Society of Japan
2014-03
application/pdf
Journal of the Physical Society of Japan
4
83
044711-1
044711-8
Journal of the Physical Society of Japan
AA00704814
00319015
https://niigata-u.repo.nii.ac.jp/record/2114/files/83_044711.pdf
eng
info:doi/10.7566/JPSJ.83.044711
http://journals.jps.jp/doi/abs/10.7566/JPSJ.83.044711
Copyright (C) 2014 The Physical Society of Japan