Metal–Insulator Transition and Superconductivity in the Two-Orbital Hubbard–Holstein Model for Iron-Based Superconductors

Abstract

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.

Phase competition in a one-dimensional three-orbital Hubbard-Holstein model

“…To date, multiorbital extensions of the HH model have received comparably less attention [35,[57][58][59][60][61]. In Ref.…”

Competing phases and orbital-selective behaviors in the two-orbital Hubbard-Holstein model

“…The single-band variant has been extensively studied, particularly at half-filling, where a direct competition occurs between antiferromagnetic Mott insulating (MI) and charge-density-wave (CDW) phases [23][24][25][26][27][28][29][30][31][32] . In comparison, far fewer studies exist for multiband generalizations of the model 14,33 . Motivated by this, we carried out a dynamical mean field theory (DMFT) 34 study of a degenerate two-orbital Hubbard-Holstein model with inequivalent bandwidths.…”

“…Methods -The Hamiltonian for the degenerate twoorbital Hubbard-Holstein model 33 is H = H kin + H lat + H e−ph + H e−e , where …”

Temperature and doping dependence of normal state spectral properties in a two-orbital model for ferropnictides

“…30 is still recognized as a useful minimal model to describe the main features of the low-energy physics of ferropnictides. [31][32][33][34][35][36][37]41,42,66 Our paper is organized as follows. In Section II A we present the microscopic correlated two-orbital model adopted for our study of the normal state of Fe-based superconductors, and describe the analytical Green's function approach we used to calculate the electronic spectral density function and the total density of states including the correlations in second-order of perturbations ( further details of our analytical calculations appear in Supplementary Appendix A).…”

“…Similar effective two-orbital models have been studied before, focusing on other aspects of the problem, mostly on the superconducting properties. For example, investigations of pairing mechanisms and gap symmetry were reported, 31-38 studies of spin fluctuations 31,32,34 and a spin-density wave phase, 39 Mott transition for strong electron correlations, [40][41][42] lattice and orbital properties, [42][43][44][45] etc. In our case, we studied the minimal microscopic two-orbital model using analytical perturbative techniques to take into account the effect of electron correlations, in order to determine the relevant normal state Green's functions and the corresponding temperature-dependent electronic spectral density.…”