Tuning Chern Number in Quantum Anomalous Hall Insulators*

The quantum anomalous Hall (QAH) effect is a two-dimensional topological insulating state that has quantized Hall resistance of h/Ce² and vanishing longitudinal resistance under zero external magnetic field, where C is called Chern number. Up to now, the zero magnetic field QAH effect has been realized only for C = 1. Here we used molecular beam epitaxy to fabricate magnetic TI multilayers and realized the well-defined QAH effect with tunable Chern number up to 5. We further demonstrated that in the same multilayer configuration, the Chern number can be tuned by varying either the Cr doping level or the thickness of the interior magnetic TI layer. One theoretical model is developed to explain our experimental observations and establish the phase diagram for the QAH effect with the tunable Chern number. Our results facilitate the applications of dissipationless chiral edge currents in energy-efficient electronic devices and open the possibility for developing multi-channel quantum computing and high-capacity chiral circuit interconnects.