Is Fermi-Surface Nesting the Origin of Superconductivity in Iron Pnictides?: A Fluctuation-Exchange-Approximation Study

We study whether Fermi-surface (FS) nesting can give rise to high-temperature superconductivity in iron pnictides. Starting with ab initio construction of an effective four-orbital model, we employ the fluctuation-exchange approximation to show that FS does not necessarily favor the stripe antiferromagnetic order observed in experiments, especially for realistic electronic correlations. If superconductivity in iron pnictides is magnetically mediated and has a fully gapped sign-reversing s-wave symmetry, our results suggest that the pairing interaction does not arise only from FS nesting and that exchange interactions between local moments in the Fe 3d orbitals may play a crucial role.