Quantum anomalous Hall effect in monolayers Ti₂X₂ (X = P, As, Sb, Bi) with tunable Chern numbers by adjusting magnetization orientation

Despite extensive research, the achievement of tunable Chern numbers in quantum anomalous Hall (QAH) systems remains a challenge in the field of condensed matter physics. Here, we theoretically proposed that Ti₂X₂ (X = P, As, Sb, Bi) can realize tunable Chern numbers QAH effect by adjusting their magnetization orientations. In the case of Ti₂P₂ and Ti₂As₂, if the magnetization lies in the x–y plane, and all C₂ symmetries are broken, a low-Chern-number phase with C = 1 will manifest. Conversely, if the magnetization is aligned to the z-axis, the systems enter a high-Chern number phase with C = 3. As for Ti₂Sb₂ and Ti₂Bi₂, by manipulating the in-plane magnetization orientation, these systems can periodically enter topological phases (C = ±1) over a 60° interval. Adjusting the magnetization orientation from +z to –z will result in the systems’ Chern number alternating between ±1. The non-trivial gap in monolayer Ti₂X₂ (X = P, As, Sb, Bi) can reach values of 23.4, 54.4, 60.8, and 88.2 meV, respectively. All of these values are close to the room-temperature energy scale. Furthermore, our research has revealed that the application of biaxial strain can effectively modify the magnetocrystalline anisotropic energy, which is advantageous in the manipulation of magnetization orientation. This work provides a family of large-gap QAH insulators with tunable Chern numbers, demonstrating promising prospects for future electronic applications.