Interfacing 2D and 3D Topological Insulators: Bi(111) Bilayer on Bi2Te3

We report the formation of a bilayer Bi(111) ultrathin film, which is theoretically predicted to be in a two-dimensional quantum spin Hall state, on a Bi2Te3 substrate. From angle-resolved photoemission spectroscopy measurements and ab initio calculations, the electronic structure of the system can be understood as an overlap of the band dispersions of bilayer Bi and Bi2Te3. Our results show that the Dirac cone is actually robust against nonmagnetic perturbations and imply a unique situation where the topologically protected one- and two-dimensional edge states are coexisting at the surface.