Tunable Topological and Magnetic Properties of MnBi₂(Te_1-xSe_x)₄

The MnBi₂Te₄ family has emerged as a class of intrinsic magnetic topological insulators exhibiting exotic transport phenomena such as the quantum anomalous Hall effect. We perform first-principles density functional theory (DFT) calculations combined with maximally localized Wannier functions for MnBi₂(Te₁₋ₓSeₓ)₄ (MBST), motivated by the most stable stacking configuration identified in recent quantum Monte Carlo simulations. In its antiferromagnetic (AFM) ground state, MBST realizes an AFM topological insulator with gapless surface states protected by the combined time-reversal and translational symmetry. In the ferromagnetic (FM) phase, MBST slabs thicker than five septuple layers exhibit Chern insulating behavior accompanied by a quantized anomalous Hall response. Our calculations confirm that the inverted band structure is preserved under moderate substitutional disorder (x ≈ 0.5–0.509), demonstrating strong defect tolerance. A systematic analysis of Se alloying in AFM-MBST reveals lattice contraction and a non-monotonic evolution of the band gap, which reaches a minimum near intermediate compositions (x ∼ 0.5). These findings suggest that MBST is a robust and tunable platform for realizing magnetic topological phases.