Study on the Valley Polarization and Quantum Properties of Two-Dimensional Pt 4 Hg 2 Cl 3 X 3 (X = F, Br)

Abstract The quantum anomalous valley Hall effect (QAVHE) represents an important research direction in topological electronics. In this work, based on first-principles calculations combined with a tight-binding (TB) model, we predict that the two-dimensional (2D) ferromagnetic material Pt 4 Hg 2 Cl 3 X 3 (X = F, Br) can realize the QAVHE. The system exhibits a Curie temperature of 219 K, and its magnetic easy axis can be tuned from the in-plane to the out-of-plane direction under biaxial strain, leading to a remarkable change in valley polarization and enabling effective control of the valley degree of freedom. A strain-driven topological phase transition from a trivial to a nontrivial state is revealed, resulting in the coexistence of the anomalous valley Hall effect (AVHE) and the quantum anomalous Hall effect (QAHE), characterized by a Chern number ( C = 1) and chiral spin-valley-locked states. The coexistence of robust valley polarization and a high Curie temperature makes this system an ideal platform for realizing dissipationless electronic transport and topological quantum computation, offering valuable prospects for the development of valleytronics, spintronics, and topological quantum materials.