Large-Gap Quantum Anomalous Hall Insulators in $A$Ti$X$ Class

TL;DR

This paper predicts that monolayer $A$Ti$X$ materials can be large-gap quantum anomalous Hall insulators with high Chern numbers, driven by $3d$-orbital band inversion due to crystal field and hopping effects.

Contribution

It introduces a new class of monolayer $A$Ti$X$ materials as potential large-gap QAH insulators with high Chern numbers, based on theoretical modeling and symmetry analysis.

Findings

Potential large-gap QAH insulators with Chern number 2 identified.

Topological band inversion driven by crystal field and hopping, not spin-orbit coupling.

Applicable to a broad class of transition metal compounds with specific space groups.

Abstract

We theoretically propose that the monolayer $A$Ti$X$ family (KTiSb, KTiBi, RbTiSb, SrTiSn) are potential candidates for large-gap quantum anomalous Hall insulators with high Chern number $\mathcal{C}=2$. Both of the topology and magnetism in these materials are from $3d$-orbitals of Ti. We construct the tight-binding model with symmetry analysis to reveal the origin of topology. Remarkably, quite different from the conventional $s$-$d$ band inversion, here the topological band inversion within $3d$ orbitals is due to the crystal field and electron hopping, while spin-orbit coupling only trivially gaps out the Dirac cone at Fermi level. The general physics from the $3d$ orbitals here applies to a large class of transition metal compounds with the space group $P4/nmm$ or $P$-$42m$ and their subgroups.