Quantum anomalous Hall effect with high Chern numbers in functionalized square-octagon Sb monolayers

Abstract The quantum anomalous Hall (QAH) effect has attracted continuous attention due to its intriguing properties and potential applications in future electronics. Here, we present our investigation of the electronic and topological properties of a square-octagon Sb monolayer with Mo atoms adsorbed (Mo@so-Sb) using first-principles calculations. Our studies reveal how a trivial insulator can be first engineered into an unusual bipolar magnetic semiconductor (BMS) and then further tuned by strain into a spintronics-favorable half semiconductor (HS) or half metal. Remarkably, with 3.7% compressive strain applied, we achieve a QAH state in Mo@so-Sb with a high Chern number (C = 4) which is much larger than that (C = ±1 or ±2) of the previously predicted Chern insulators. This QAH state is characterized by the appearance of four gapless chiral edge states within the nontrivial band gap, enabling a robust multi-channel low-power-consumption transport. Its nontrivial topology primarily originates from the band inversion between the non-degenerate Mo 4d and Sb 5p orbitals. Additionally, we demonstrate the interesting BMS, HS, and QAH states can be controlled by the Mo adsorption concentrations. Our findings not only provide a versatile means of transforming trivial insulators into the desired spintronics-favorable and topological states, but also open new possibilities for high-performance electronic devices.