The valley degree of freedom, as an intrinsic electronic property analogous to charge and spin, has emerged as a promising carrier of information in next-generation low-power and high-efficiency electronic devices. Achieving robust and controllable valley polarization is a central challenge in the development of valleytronics. Ferrovalley materials, characterized by intrinsic magnetic ordering that breaks time-reversal symmetry, are particularly attractive because they can generate spontaneous valley polarization without the need for external fields. In this work, based on first-principles calculations within the framework of density functional theory, we systematically investigate the structural stability, magnetic properties, electronic structure, and valley polarization behavior of a two-dimensional CeBr₂ monolayer.
Our results demonstrate that monolayer CeBr₂ possesses excellent thermodynamic and dynamical stability, as confirmed by total energy analysis and phonon dispersion calculations. The system exhibits a ferromagnetic ground state with a Curie temperature exceeding room temperature, indicating its suitability for practical applications. In addition, a pronounced in-plane magnetic anisotropy is identified, which plays a crucial role in stabilizing long-range magnetic order in two-dimensional systems. When spin–orbit coupling is taken into account, the degeneracy between the K and K′ valleys is lifted, leading to a spontaneous valley splitting at the valence band maximum. The magnitude of this splitting is significantly larger than the thermal fluctuation energy at room temperature, ensuring robust valley polarization under ambient conditions. Furthermore, Berry curvature calculations reveal the presence of nonzero anomalous Hall conductivity and spin Hall conductivity near the valley regions, indicating that monolayer CeBr₂ can host the anomalous valley Hall effect and related spin-dependent transport phenomena. These features highlight the coexistence and coupling of multiple degrees of freedom, including charge, spin, orbital, and valley, in this system.
To explore the tunability of its physical properties, we further investigate the effects of electron correlation and external strain. By varying the Hubbard U parameter, we find that enhanced electron correlation strengthens both magnetic anisotropy and valley polarization, reflecting the important role of localized 4f electrons of Ce atoms. Meanwhile, the application of biaxial strain within a range of ±5% enables continuous modulation of valley splitting and magnetic anisotropy without altering the ferromagnetic ground state, demonstrating excellent mechanical and functional robustness. Overall, this study identifies monolayer CeBr₂ as a promising two-dimensional ferrovalley material with large valley polarization, high thermal stability, and strong tunability. The results provide valuable insights into the interplay between electron correlation, spin–orbit coupling, and lattice deformation, and offer theoretical guidance for the design and optimization of multifunctional valleytronic and spintronic devices based on rare-earth halide systems.