Giovanny Espitia Qualifier

Strongly correlated and excitonic phenomena in moiré materials depend on flat electronic bands

and exciton–phonon coupling. Flat bands typically appear at small twist angles, but we report

flat bands with a quasi-one-dimensional, taco-shaped dispersion in twisted bilayer WSe₂ at the

large angle of 21.8°

. First-principles calculations trace them to optimal interlayer hybridization

between like-spin λ valleys, forming six anisotropic channels with alternating spin polarization

reminiscent of altermagnetic textures. A sharp van Hove singularity marks band flattening at the

conduction band minimum, explaining recently observed phonon-assisted intervalley absorption

peaks. How moiré superlattices modify exciton–phonon coupling, which governs exciton

relaxation, linewidths, and transport, remains largely unexplored. We extend the pristine unit-cell

matrix projection (PUMP) approach [1], which scales GW–Bethe–Salpeter calculations to large

moiré cells, to describe coupling between moiré excitons and spatially modulated moiré

phonons.

[1] Naik, Regan, Zhang, et al., Nature 609, 52–57 (2022)