Quantum anomalous Hall effect and proximity coupling effect induced valley polarization in Ti3STe4 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.