Interaction-induced singular Fermi surface in a high-temperature oxypnictide superconductor

TL;DR

This paper reveals that in a high-temperature iron-based superconductor, the Fermi surface features singularities caused by electronic interactions, which significantly influence superconductivity and correlate with the highest transition temperatures.

Contribution

It demonstrates that the Fermi surface in SmFe0.92Co0.08AsO deviates from the typical nesting scenario, featuring singularities that impact low-energy electronic properties and superconductivity.

Findings

Fermi surface contains singular constructs from band edges.

Singularities are pulled to the Fermi level by electronic interactions.

Occurrence of singularities correlates with maximum Tc in iron-based superconductors.

Abstract

In the family of iron-based superconductors, LaFeAsO-type materials possess the simplest electronic structure due to their pronounced two-dimensionality. And yet they host superconductivity with the highest transition temperature Tc=55K. Early theoretical predictions of their electronic structure revealed multiple large circular portions of the Fermi surface with a very good geometrical overlap (nesting), believed to enhance the pairing interaction and thus superconductivity. The prevalence of such large circular features in the Fermi surface has since been associated with many other iron-based compounds and has grown to be generally accepted in the field. In this work we show that a prototypical compound of the 1111-type, SmFe0.92Co0.08AsO, is at odds with this description and possesses a distinctly different Fermi surface, which consists of two singular constructs formed by the edges of several bands, pulled to the Fermi level from the depths of the theoretically predicted band structure by strong electronic interactions. Such singularities dramatically affect the low-energy electronic properties of the material, including superconductivity. We further argue that occurrence of these singularities correlates with the maximum superconducting transition temperature attainable in each material class over the entire family of iron-based superconductors.