Dirac Band Engineering of Topological Insulator/Graphene Hybrid Structures*

Dirac materials such as graphene and topological insulators (TI) have attracted much attention because of their unique electrical properties. Stacking these two Dirac materials to form a heterostructure provides a platform for the exploration of the interesting physics of coupled Dirac fermions. We recently used molecular beam epitaxy to fabricate the (Bi_1-xSb_x)₂Te₃/graphene hybrid structures and systematically studied the electronic band structures as a function of x and thickness. Because the ratio between the lattice constants of Sb₂Te₃ and graphene is √3, the Dirac cone of graphene can be folded to the Γ point of the Brillouin zone of Sb₂Te₃. The coexistence of two different Dirac low-energy states is indeed observed in angle-resolved photoemission spectroscopy measurements. This phenomenon is further demonstrated by scanning tunneling microscopy results and first-principles calculations. Our work is of great importance for understanding the interplay of Dirac fermions across the TI/graphene interface and paves a new way to study band engineering in Dirac materials.