二维过渡金属三元硫属化合物中实现量子反常霍尔效应的理论设计

A generic designing rule for realizing quantum anomalous Hall phase in a transition-metal trichalcogenide family

区别于在三维拓扑绝缘体引入磁性的设计思路,在二维铁磁材料中引入拓扑特性是实现量子反常霍尔效应(QAHE)的一种新途径.最近实验成功制备的二维铁磁绝缘体为实现该效应提供了新的契机.本文基于密度泛函理论的第一性原理计算,设计了一个在过渡金属三元硫属化合物Cr2A2X6(其中A=Si,Ge,Sn;X=S,Se,Te)中实现QAHE的普适规则.该设计原则是,通过适当的表面修饰可将二维非拓扑的磁性绝缘体转变为量子反常霍尔体系.以硅烯修饰的Cr2Sn2Se6(Si/Cr2Sn2Se6)为例,计算发现Cr2Sn2Se6单层的居里温度可提高至92 K.具体的电子能带和拓扑性质计算发现,Si/Cr2Sn2Se6异质结存在约30 meV的拓扑非平庸带隙,即该体系中可以实现QAHE.进一步的低能有效模型分析表明,Si/Cr2Sn2Se6的拓扑特性是由Cr2A2X6六角晶格中的Cr原子贡献的.此外,还发现其他Cr2A2X6通过表面修饰也可以实现QAHE.以上研究结果证实了本文方案的普适性,其为实现高温QAHE提供了新的理论指导.

Different from introducing ferromagnetism in three-dimensional(3D) topological insulators, empowering nontrivial band topology with 2D ferromagnetic(2DFM)materials is another way to realize quantum anomalous Hall effect(QAHE). The recently discovered 2DFM insulators provide unprecedented opportunities for realizing such an intriguing quantum phenomenon. Here, by using first-principles approaches, we design a generic rule for realizing QAHE in the transition-metal trichalcogenide family materials of Cr2A2X6(where A = Si, Ge, Sn;X = S, Se, Te), whose design principle is based on that a 2D topologically trivial magnetic insulator can be converted into a QAH system via proper surface modification. Taking silicene-passivated Cr2Sn2Se6as an illustration, we show that the Cuire temperature of Cr2Sn2Se6monolayer can be enhanced up to ~92 K after silicene passivation. Most strikingly, such a heterostructure harbors QAHE with a band gap of ~30 meV. Further low-effective model analyses reveal that the topologically nontrivial states are attributed to the honeycomb lattice of Cr atoms. All those results demonstrate that our proposal is general, which opens a new avenue to explore high-temperature QAHE.