FeTaX2: A ferrimagnetic quantum anomalous Hall insulator

Abstract

We propose that the van der Waals layered ternary transition metal chalcogenides FeTa$X_2$ ($X=$ S, Se, Te) as a new family of ferrimagnetic quantum anomalous Hall insulators with a sizable bulk gap and high Chern number $C=-2$. The magnetic order arises primarily from Fe atoms, whose strong ferromagnetic exchange induces moments on neighboring Ta sites. The large topological gap originates from a \emph{deep} $s$-$d$-type band inversion between spin-down Ta $d_{z^2}$ and $d_{xy}$ orbitals near the Fermi level-a mechanism unique to $d$-orbital systems. Remarkably, the Curie temperature of monolayer FeTa$X_2$ is predicted to significantly exceed that of monolayer MnBi$_2$Te$_4$. Furthermore, both the Curie temperature and topological gap scale positively with the spin-orbit coupling strength of the $d$ electrons, suggesting a common physical origin. Owing to its structural similarity to Fe$X$ superconductors and reduced net magnetization, FeTa$X_2$ further offers a promising platform for realizing chiral topological superconductivity. These findings, if realized experimentally, could open new avenues for the research and application of topological quantum physics.