Multimechanism Quantum Anomalous Hall and Chern Number Tunable States in Germanene (silicene, Stanene)/mbi_2te_4 Heterostructures

By constructing germanene (silicene, stanene)/ M Bi 2 Te 4 ( M = 3 d -transition elements) heterostructures, we discovered and designed multimechanism quantum -anomalous -Hall (QAH) systems, including r -based QAH, K - K ' -connected QAH, and valley -polarized K - or K ' -based QAH states via first -principle computations. The unique systems possess a global gap and tunable Chern number. The coexisting conventional r -based QAH state of M Bi 2 Te 4 and valley -polarized K ( K ' )-based QAH state of germanene (silicene, stanene), with opposite chirality, can interact with each other. Adjusting magnetic configurations of M Bi 2 Te 4 -layers not only switch on (off) the QAH conductance, but also modulate Chern numbers exactly. For example, the germanene/bilayerNiBi 2 Te 4 possesses the Chern number C = + 1 in ferromagnetic couplings and C = + 2 in antiferromagnetic couplings. The novel multimechanism QAH insulators, which are achievable in experiments, provide a new approach to spintronics and valleytronics based on topological states of matter.