From density functional theory to the functional renormalization group: superconductivity in the iron pnictide LiFeAs

TL;DR

This paper combines density functional theory and the functional renormalization group to analyze superconductivity in LiFeAs, revealing the dominant role of antiferromagnetic fluctuations in driving s+- pairing.

Contribution

It introduces a novel combined method incorporating orbital-dependent interactions to study weakly to intermediately correlated Fermi systems, applied specifically to LiFeAs.

Findings

Superconductivity in LiFeAs is driven by collinear antiferromagnetic fluctuations.

The s+- superconducting order parameter is identified as the dominant pairing symmetry.

Ferromagnetic fluctuations are less influential than antiferromagnetic ones in this system.

Abstract

A combined density functional theory and functional renormalization group method is introduced which takes into account orbital-dependent interaction parameters to derive the effective low-energy theory of weakly to intermediately correlated Fermi systems. As an application, the competing fluctuations in LiFeAs are investigated, which is the main representative of the 111 class of iron pnictides displaying no magnetic order, but superconductivity, for the parent compound. The superconducting order parameter is found to be of s+- type driven by collinear antiferromagnetic fluctuations. They eventually exceed the ferromagnetic fluctuations stemming from the small hole pocket at the Gamma point, as the system flows to low energies.