Quantum anomalous Hall effect and proximity coupling effect induced valley polarization in Ti 3 STe 4 monolayer

The search of quantum anomalous Hall (QAH) effect and other Hall effects is promising for developing high-performance electronic and spintronic devices. By employing the first-principles calculations, we find the existence of QAH effect and valley Hall effect in two-dimensional (2D) ${\mathrm{Ti}}₃{\mathrm{STe}}₄$ monolayer. The ${\mathrm{Ti}}₃{\mathrm{STe}}₄$ monolayer is a robust Weyl half metal with the Weyl point protected by vertical mirror symmetry ${M}_v$. By considering the spin orbital coupling (SOC) effect, the monolayer is transformed to be a QAH insulator with a sizable band gap. More remarkably, the valley-polarized quantum anomalous Hall (VP-QAH) state is realized in ${\mathrm{Ti}}₃{\mathrm{STe}}₄$/${\mathrm{Sc}}₂{\mathrm{CO}}₂$ heterostructure due to the broken combined mirror symmetry $({M}_v)$ and time reversal symmetry (T). Through the development of a spinless three-band tight-binding model based on first-principles calculations, we reproduce density functional theory results and provide insight into the emergence of the VP-QAH state. Our findings greatly enrich the research on QAH and VP-QAH physics and their potential application on spintronic devices.