Quantum Anomalous Hall Effect in Low-Buckled Honeycomb-Lattice Structures from In-Plane Magnetization

We theoretically report that the quantum anomalous Hall effect (QAHE) can be realized in \textit{low-buckled} honeycomb-lattice systems with time-reversal symmetry broken from in-plane magnetization. We find that both the intrinsic and intrinsic-Rashba spin-orbit couplings in the low-buckled honeycomb-lattice structures are crucial in the QAHE formation. We show that the topologically nontrivial bulk gap harbouring a QAHE with Chern number $\mathcal{C}=\pm1$ opens in the vicinity of the saddle point $M$, where the strong anisotropy makes our proposal completely different from previous ones based on the isotropic Dirac bands. We further show that the QAHE with gate-tunable Chern number can be achieved in Bernal-stacked multilayer systems, and the applied electrical gating can also dramatically decrease the critical magnetization to make the QAHE experimentally feasible.