Large-gap quantum anomalous Hall insulators in the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>A</mml:mi><mml:mi>Ti</mml:mi><mml:mi>X</mml:mi></mml:math> (<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>A</mml:mi><mml:mo>=</mml:mo><mml:mi mathvariant="normal">K</mml:mi></mml:math>, Rb, Sr; <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>X</mml:mi></mml:math>=Sb, Bi, Sn) class of compounds
Yadong Jiang, Huan Wang, Jing Wang
Abstract
Quantum anomalous Hall insulators provide an intriguing platform to study emergent magnetic topological phenomena, but the low critical temperature is a weighty obstacle for practical applications. We theoretically propose that the monolayer $A\mathrm{Ti}X$ family (KTiSb, KTiBi, RbTiSb, SrTiSn) are potential candidates for large-gap quantum anomalous Hall insulators with high Chern number $\mathcal{C}=2$. Both the topology and the magnetism in these materials are from $3d$ orbitals of Ti. We further construct the tight-binding model from orbital projected band structure and symmetry analysis to reveal the origin of topology. Remarkably, quite different from the conventional $s\text{\ensuremath{-}}d$ 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 $P\text{\ensuremath{-}}42m$ and their subgroups. These notable predictions, if realized experimentally, could greatly promote the research and application of topological quantum physics.