Three- and two-dimensional topological insulators in Pb2Sb2Te5, Pb2Bi2Te5, and Pb2Bi2Se5 layered compounds

The electronic structure of ternary compounds Pb2Sb2Te5, Pb2Bi2Te5, and Pb2Bi2Se5, which have a layered structure that consists of nine-layer atomic blocks separated by van der Waals gaps, has been theoretically studied. It has been shown that all studied compounds are three-dimensional topological insulators. The possibility of the existence of a two-dimensional topological insulator has been found in ultrathin (0001) Pb2Sb2Te5 and Pb2Bi2Te5 films. Oscillations of the acurrency sign(2) topological invariant with an increase in the film thickness have been observed in the latter compound.