Tunable giant anomalous Hall effect in bilayer magnetic topological insulator

Abstract In the two-dimensional limit, the intrinsic magnetic topological insulator MnBi 2 Te 4 offers an exceptional platform for probing novel quantum states and their response to external perturbations. Using first-principles calculations and classical Heisenberg Monte Carlo simulations, we demonstrate that electrostatic gating and surface chemical functionalization trigger a remarkable crossover from the topological to the conventional anomalous Hall regime. This transition is governed by the simultaneous shift of the Fermi level and an antiferromagnetic-to-ferromagnetic reversal of interlayer coupling. Notably, hole doping drives the Fermi level deep into the valence bands, unlocking Berry curvature hot spots that generate an exceptionally high anomalous Hall conductivity of 1380 S/cm. Conversely, surface chemical functionalization preserves a Chern band manifold coexisting with metallic states, where intrinsic σ xy is reduced from e 2 /h to ∼ 0.86 e 2 /h due to the spectral coexistence of a chiral edge mode with the metallic bulk states of the two-dimensional film. Critically, both tuning strategies significantly strengthen in-plane exchange interactions, driving a substantial increase in the magnetic ordering temperature compared to the pristine bilayer. These findings establish a powerful, versatile strategy to concurrently tailor the topological, magnetic, and transport properties of ultrathin MnBi 2 Te 4 , advancing the design of reconfigurable quantum devices.