Proximity-induced giant spin-orbit interaction in epitaxial graphene on a topological insulator

Heterostructures of Dirac materials such as graphene and topological insulators provide interesting platforms to explore exotic quantum states of electrons in solids. Here we study the electronic structure of the graphene-Sb₂Te₃ heterostructure using density functional theory and tight-binding methods. We show that the epitaxial graphene on Sb₂Te₃ turns into the quantum spin-Hall phase due to its proximity to the topological-insulating Sb₂Te₃. It is found that the epitaxial graphene develops a giant spin-orbit gap of about {~}20 meV, which is about three orders of magnitude larger than that of pristine graphene. We discuss the origin of such enhancement of the spin-orbit interaction and possible outcomes of the spin-Hall phase in graphene.