Trigonal Warping Induced Multiple Topological Phase Transitions in Janus Monolayer MoTe2 XY ( X, Y = F, Cl, Br)

Realizing multiple topological quantum states within a single two-dimensional (2D) system by tuning bands near the Fermi level via external fields remains challenging. Using a low-energy effective k·p model, we find that trigonal warping induces additional band inversion points, driving multiple topological phase transitions under applied electric fields. We identify 2D ferromagnetic Janus monolayers MoTe2XY (X, Y = F, Cl, Br) as ideal candidates. In MoTe2FBr, Rashba spin–orbit coupling inherently induces trigonal warping. Its ground state is a quantum anomalous Hall insulator with Chern number C = 2. Applying an out-of-plane electric field drives successive transitions to C = 1 and ultimately C = 0. Remarkably, the C = 0 phase is a higher-order topological insulator protected by C3 symmetry, characterized by robust corner states and an orbital Hall-conductivity plateau. Our work highlights trigonal warping’s crucial role in topological transitions and proposes a versatile platform for quantum devices.