اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدMetal-insulator transition and superconductivity in the two-orbital Hubbard-Holstein model for iron-based superconductors
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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, $chi_{s}$ and $chi_{o}$, increase with $chi_{s}=chi_{o}$ in the absence of the Hunds rule coupling $J$ and the electron-phonon coupling $g$. In the presence of $J$ and $g$, there are distinct two regimes: for $J stackrel{>}{_sim} 2g^2/omega_0$ with the phonon frequency $omega_0$, $chi_{s}$ is enhanced relative to $chi_{o}$ and shows a divergence at $J=J_c$ above which the system becomes Mott insulator, while for $J stackrel{<}{_sim} 2g^2/omega_0$, $chi_{o}$ is enhanced relative to $chi_{s}$ 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.
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