Proximity exchange induced gap opening and topological feature in graphene/1T′-MX₂ (M = Mo,W; X = S,Se,Te) Dirac heterostructures

By using first-principles calculations, we demonstrate the influence of proximity effect on the band structures of heterostructures formed by graphene stacking on a two dimensional (2D) topological insulator (TI) 1T′-MX₂. The interlayer distance d between graphene and TI decreases with the enhancement of the intrinsic lattice anisotropy of 1T′-MX₂, which determines different strength of the interlayer proximity interaction. The bandgap can be opened by the proximity exchange. The weak anisotropic symmetry of heterostructure (large d) only results in a small band gap (∼50 meV) in graphene/MoTe₂. However, a large energy gap (up to ∼200 meV) can be obtained in graphene/MoS₂, which is attributed to the inter-intralayer charge transfer due to the strong proximity interaction of the hetero-interface (small d). In addition, the 1T′-MX₂ of heterostructure still possesses the topological feature of Z₂ = 1, since the graphene has a negligible effect on the band structure of the system.