Valley topological phase transitions under the combined effects of electronic correlation and strain in the H-TiSeBr monolayer†

The valley-polarized quantum anomalous Hall (VP-QAH) effect induced by external fields (such as strain) has attracted widespread attention as an emerging physical phenomenon. In this paper, we predict through first-principles calculations that the H-TiSeBr monolayer is a room-temperature ferromagnetic semiconductor with a Curie temperature of 350 K. When the magnetization direction is perpendicular to the plane, a valley polarization of 56.95 meV arises in the conduction band. Interestingly, under compressive strains of −1.32% and −1.165%, the material exhibits two half-valley metal (HVM) states. Between these two HVM states, the band inversion between d_xy + d_x²−y² and d_z² at the −K valley leads to the emergence of the valley-polarized quantum anomalous Hall (VP-QAH) phase. Further research reveals that the reduced electronic correlation enables the H-TiSeBr monolayer to maintain the VP-QAH phase over a broader strain range. Combined with k·p model analysis, we demonstrate that this phenomenon primarily arises from the decreased −K (K) to −K (K) deformation potential constant induced by the decrease of the electronic correlation. Our findings provide new insights for manipulating valleytronics and enhancing the fundamental understanding of valley-related physical mechanisms.