Ab initio Studies of Magnetism in the Iron Chalcogenides FeTe and FeSe

TL;DR

This study uses ab initio methods to investigate the magnetism in FeTe and FeSe, revealing the importance of eliminating double counting in electron correlations to accurately reproduce magnetic orders and degeneracies.

Contribution

The paper introduces an ab initio low-energy effective model with a constrained GW method that accurately captures magnetic properties of FeTe and FeSe.

Findings

Reproduces bicollinear antiferromagnetic order in FeTe

Shows degeneracy of magnetic orders in FeSe

Explains absence of magnetic order in FeSe

Abstract

The iron chalcogenides FeTe and FeSe belong to the family of iron-based superconductors. We study the magnetism in these compounds in the normal state using the ab initio downfolding scheme developed for strongly correlated electron systems. In deriving ab initio low-energy effective models, we employ the constrained GW method to eliminate the double counting of electron correlations originating from the exchange correlations already taken into account in the density functional theory. By solving the derived ab initio effective models, we reveal that the elimination of the double counting is important in reproducing the bicollinear antiferromagnetic order in FeTe, as is observed in experiments. We also show that the elimination of the double counting induces a unique degeneracy of several magnetic orders in FeSe, which may explain the absence of the magnetic ordering. We discuss the relationship between the degeneracy and the recently found puzzling phenomena in FeSe as well as the magnetic ordering found under pressure.