The coexistence of valley polarization and topology has considerably facilitated the applications of 2D materials toward valleytronics device technology. However, isolated and distinct valleys are required to observe the valley-related quantum phenomenon. Herein, we report a new mechanism to generate in-plane magnetization direction-dependent isolated valley carriers by preserving or breaking the mirror symmetry in a 2D system. First-principle calculations are carried out on a prototype material, W2MnC2O2 MXene, to demonstrate the mechanism. A valley-coupled topological phase transition among Weyl semimetal, valley-polarized quantum anomalous Hall insulator, and topological semimetal is observed by manipulating the in-plane magnetization directions in W2MnC2O2. Monte Carlo simulations of W2MnC2O2 show that the estimated Curie temperature is around 170 K, indicating the possibility of observing valley-polarized topological states at higher temperatures. Our finding provides a generalized platform for investigating the valley and topological physics, which is extremely important for future quantum information processing applications.
Keywords: in-plane magnetization; mirror symmetry; quantum anomalous Hall effect; search rule; topological phases; valley polarization.