Geometric origins of topological insulation in twisted layered semiconductors

Twisted bilayers of two-dimensional (2D) materials are proving a fertile ground for investigating strongly correlated electron phases. This is because the moire pattern introduced by the relative twist between layers introduces long-wavelength effective potentials which lead to electron localization. Here, we develop a generalized continuum model for the electronic structure of moire patterns, based on first-principles calculations and tailored to capture the physics of twisted bilayer 2D semiconductors. We apply this model to a database of eighteen 2D crystals covering a range of atomic relaxation and electronic structure features. Many of these materials host topologically insulating (TI) moire bands in a certain range of twist angles, which originate from the competition between triangular and hexagonal moire patterns, tuned by the twist angle. The topological phases occur in the same range as the maximally flat moire bands.