Band renormalization and Fermi surface reconstruction in iron-based superconductors

TL;DR

This paper investigates how Coulomb interactions and spin fluctuations influence band structure, Fermi surface topology, and pairing symmetry in iron-based superconductors using a three-orbital model and fluctuation exchange approximation.

Contribution

It demonstrates the orbital-dependent band renormalization and Fermi surface evolution due to inter-orbital spin fluctuations in iron-based superconductors.

Findings

Fermi surface topology varies with doping, matching experiments.

Inter-orbital spin fluctuations cause anisotropic band renormalization.

Superconducting pairing has extended s-wave symmetry.

Abstract

Using the fluctuation exchange approximation and a three-orbital model, we study the band renormalization, Fermi surface reconstruction and the superconducting pairing symmetry in the newly-discovered iron-based superconductors. We find that the inter-orbital spin fluctuations lead to the strong anisotropic band renormalization and the renormalization is orbital dependent. As a result, the topology of Fermi surface displays distinct variation with doping from the electron type to the hole type, which is consistent with the recent experiments. This shows that the Coulomb interactions will have a strong effect on the band renormalization and the topology of the electron Fermi pocket. In addition, the pairing state mediated by the inter-orbital spin fluctuation is of an extended s-wave symmetry.