Theoretical study of twisted bilayer Bi₂(Te,Se)₃

Recently, Moiré superlattice systems, such as twisted bilayer graphene, have been very actively studied.

Here, we propose twisted bilayer Bi₂(Te,Se)₃ as a new Moiré superlattice system and show a result of our theoretical study on its novel topological properties. Untwisted Bi₂(Te,Se)₃ is one of the well-known topological insulators, and it is reported that the topological invariant of a thin film Bi₂(Te,Se)₃ strongly depends on the number of stacked layers. By driving the stacking-dependent phase transition with Moiré superlattice structure, we show a twisted bilayer Bi₂(Te,Se)₃ has topological insulator domains and normal insulator domains in the Moiré unit cell. We also show there are corresponding edge states at the domain boundaries, and they are quantized by a finite size effect of the boundaries and result in Moiré flat bands. Moreover, in the Moiré band structure, we have obtained topological insulator phases with Moiré scale edge states that emerge from the domain-boundary edge states.