Moire induced topology and flat bands in twisted bilayer WSe2: A first-principles study

We study the influence of strong spin-orbit interaction on the formation of flat bands in relaxed twisted bilayer WSe2. Flat bands, well separated in energy, emerge at the band edges for twist angles theta near 0 degrees and 60 degrees. For theta near 0 degrees, the interlayer hybridization together with a moire potential determines the electronic structure. The bands near the valence band edge have nontrivial topology, with Chern numbers equal to +1 or -1. We propose that the nontrivial topology of the first band can be probed experimentally for twist angles less than a critical angle of 3.5 degrees. For theta near 60 degrees, the flattening of the bands arising from the K point of the unit cell Brillouin zone is a result of atomic rearrangements in the individual layers. Our findings on the flat bands and the localization of their wave functions for both ranges of theta match well with recent experimental observations.

Automated summary

We study the influence of strong spin-orbit interaction on the formation of flat bands in relaxed twisted bilayer WSe2. Flat bands emerge at twist angles near 0 degrees and 60 degrees, with the electronic structure being determined by interlayer hybridization and a moire potential for angles near 0 degrees, and by atomic rearrangements in the individual layers for angles near 60 degrees. Our findings match well with recent experimental observations.