Mixed-dimensional graphene/Sn_xPb_1-xTe heterostructures: electronic structure properties from first principles

Moiré superstructures involving mixed-dimensional (2D and 3D) materials are expected to result in novel electronic properties that are potentially just as interesting as those found by moiré engineering of interfaces between 2D layered materials. In this context, the interface between graphene and SnTe is especially interesting since both the materials separately exhibit remarkable properties, such as the Dirac cones of graphene and topological electronic surface states of SnTe. As shown recently, a graphene/Sn_xPb_1-xTe (111) heterostructure exhibits carrier mobilities and magnetoresistance greater than either material alone [1]. To understand the physics behind these experiments, we have studied the electronic properties of the graphene/Sn_xPb_1-xTe heterostructure, in which a graphene monolayer is in van der Waals contact with a Te-terminated surface of lead-doped SnTe. We found that adding enough lead, destroys the SnTe topological surface states. However, since the (111) surface is polar, alternate metallic surface states are created in SnPbTe due to partial filling of the surface states. Our ab initio calculations show that these surface states, under graphene, are not confined to very top layer but extend into the bulk region over approximately 10 layers. This 2D electron gas created in the system under discussion is similar to that found at the LaAlO₃/SrTiO₃ interface, and can explain the experimental observations of Ref. [1].



[1] G. M. Stephen et al., Magnetotransport in graphene/Pb_0.24Sn_0.76Te heterostructures: finding a way to avoid catastrophe, ACS Nano, to be published (2022).