Topological interface states in the natural heterostructure (PbSe)(5)(Bi2Se3)(6) with Bi-Pb defects

We study theoretically the electronic band structure of (PbSe)(5)(Bi2Se3)(6), which consists of an ordinary insulator PbSe and a topological insulator Bi2Se3. The first-principles calculations show that this material has a gapped Dirac-cone energy dispersion inside the bulk, which originates from the topological states of Bi2Se3 layers encapsulated by PbSe layers. Furthermore, we calculate the band structures of (BixPb1-x Se)(5)(Bi2Se3)(6) with Bi-Pb antisite defects included in the PbSe layers. The result shows that a high density of Bi-Pb defects can exist in real materials, consistent with the experimentally estimated x of more than 30%. The BiPb defects strongly modify the band alignment between Bi2Se3 and PbSe layers, while the topological interface states of Bi2Se3 are kept as a gapped Dirac-cone-like dispersion.