Extended Hubbard model of superconductivity driven by charge fluctuations in iron-pnictides

Abstract

We present a scenario for iron-pnictide superconductivity mediated by charge fluctuations that are strongly enhanced by Fe-As intersite electronic interactions. Deriving an eight-band extended Hubbard model including Fe 3$d$ and As 4$p$ orbitals for the LaOFeAs family, we show that charge fluctuations induced by $p$-$d$ charge transfer and As orbital polarization interactions in the Fe-pnictogen structure peak at wavevectors $(0, 0)$, and ($π$, 0) and ($π$, $π$) respectively. Intraorbital spin-singlet pairing attraction develops at these wavevectors and the solution of the linearized gap equation shows robust s-wave superconductivity with both $s_\pm$ and $s_{++}$ gap functions.

revised version, to be published in Phys. Rev. B as a rapid communication. 5 pages, 4 eps figures and 1 table