Topological interface states in the natural heterostructure (PbSe)s(Bi_2Se_3)_6 with Bi_(Pb) defects

摘要

We study theoretically the electronic band structure of (PbSe)_5 (Bi_2Se_3)_6, which consists of an ordinary insulator PbSe and a topological insulator Bi_2Se_3. 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 Bi_2Se_3 layers encapsulated by PbSe layers. Furthermore, we calculate the band structures of (Bi_xPb_(1-x)Se)_5(Bi_2Se_3)_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 Bi_(pb), defects strongly modify the band alignment between Bi_2Se_3 and PbSe layers, while the topological interface states of Bi_2Se_3 are kept as a gapped Dirac-cone-like dispersion.