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

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 3d and As 4p 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 wave vectors (0,0), and (pi, 0) and (pi, pi), respectively. Intraorbital spin-singlet pairing attraction develops at these wave vectors and the solution of the linearized gap equation shows robust s-wave superconductivity with both s(+/-) and s(++) gap functions.