Magnetism and symmetry of superconducting gap in LaFeAsO from dynamical mean-field theory

TL;DR

This study uses DFT+DMFT to analyze how electronic correlations influence magnetism and superconductivity in LaFeAsO, revealing a dominant s± pairing symmetry unaffected by dynamic correlations.

Contribution

It demonstrates that dynamic correlation effects do not alter the leading superconducting instability in LaFeAsO, emphasizing the role of itinerant electrons.

Findings

Peak in static susceptibility at Q=(π,π) indicating magnetic instability

Close competition between d-wave and s± pairing symmetries

Dynamic correlations do not change the leading superconducting instability

Abstract

By employing a combined method of density functional theory and dynamical mean field theory (DFT+DMFT) we investigate the effect of electronic correlations on the magnetic and superconducting properties of the iron-based parent compound LaFeAsO. We find that the static non-local susceptibility $\chi({\bf q})$ exhibits a peak at the in-plane wave vector ${\mathbf Q}=(\pi,\pi)$, which is strongly enhanced upon inclusion of the vertex corrections in the ladder approximation, leading to magnetic instability. Considering the eigenfunctions of the Bethe-Salpeter equation with the vertex, obtained within the second order perturbation theory, as well as the ladder approach containing dynamic interaction vertices, in agreement with earlier weak-coupling-based studies of LaFeAsO, we obtain a close competition between $d$-wave and $s_{\pm}$ order parameters, dominating in the second-order and ladder approach, respectively. We argue that the dominating $s_{\pm}$ instability in the ladder DFT+DMFT approach is related to the reduced degree of magnetic frustration by itinerant degrees of freedom due to only partially formed local magnetic moments. Our study shows that dynamic correlation effects do not change the type of the leading superconducting instability in LaFeAsO.