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

TL;DR

This paper proposes that charge fluctuations, enhanced by intersite interactions in an extended Hubbard model, can mediate s-wave superconductivity in iron-pnictides, with specific pairing symmetries identified.

Contribution

The study introduces an eight-band extended Hubbard model for iron-pnictides showing charge fluctuations can lead to s-wave superconductivity with distinct gap structures.

Findings

Charge fluctuations peak at specific wavevectors in the Fe-As structure.

Intraorbital spin-singlet pairing attraction develops at these wavevectors.

Robust s-wave superconductivity with $s_$ and $s_{++}$ gap functions is predicted.

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 ($\pi$, 0) and ($\pi$, $\pi$) 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.