One-Dimensional Flat Bands and Anisotropic Moiré Excitons in Twisted Tin Sulfide Bilayers

Group IV monochalcogenides have attracted significant recent attention due to their similarities to black phosphorus and their potential applications in “twistronics”, inspired by the synthesis of nanowires and nanocrystals with continuous interlayer Eshelby twists. They are also proposed as an ideal platform to study strongly correlated physics with dimensional crossover. However, little is known on moiré superlattices formed by twisted monochalcogenide bilayers. In particular, the optoelectronic properties of the twisted monochalcogenide bilayers are largely unexplored and it is not clear whether moiré excitons can be hosted in such bilayers. In this work, we reveal the structural, optoelectronic, and excitonic properties of twisted SnS bilayers from first-principles. The key aspects of the moiré superlattices, including lattice reconstructions, moiré potentials, formation of flat bands, one-dimensional and anisotropic moiré excitons, and tuning of moiré excitons by twist angle and interlayer distance, are examined.