Multimechanism quantum anomalous Hall and Chern number tunable states in germanene (silicene, stanene)/$M$Bi${}_2$Te${}_4$ heterostructures

Abstract

By constructing germanene (silicene, stanene)/$M$Bi${}_2$Te${}_4$ ($M$ = 3d-transition elements) heterostructures, we discovered and designed multimechanism quantum-anomalous-Hall (QAH) systems, including $\hat{I}“$-based QAH, $K$-$K^{\prime }$-connected QAH, and valley-polarized $K$- or $K^{\prime }$-based QAH states via first-principle computations. The unique systems possess a global gap and tunable Chern number. The coexisting conventional $\hat{I}“$-based QAH state of $M$Bi${}_2$Te${}_4$ and valley-polarized $K$($K^{\prime }$)-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/bilayer-NiBi${}_2$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.

9 pages, 4 figures