In the large family of 2D materials, in-plane anisotropic materials exhibit direction-dependent properties due to their different structural orientations (armchair and zigzag). We focus on monochalcogenides (such as GeSe or SnSe), which have strong van der Waals bonds between layers and high exfoliation energies. These monochalcogenides are explored for their promising applications in thermoelectric and photovoltaic devices. Their structural anisotropy leads to anisotropy in their electrical and optical properties. We can enhance this anisotropy by stacking these materials and preparing bilayer heterostructures.

According to theoretical calculations, stacking monolayer GeSe will introduce one-dimensional flat bands, which could help create bound excitons in nearly one-dimensional dimensions. Novel physical phenomena are expected if we stack these materials in the monolayer limit. However, there is a lack of research on the moiré effect and interlayer emission from the heterostructures of these materials.

Useful References:
Kennes, D.M., Xian, L., Claassen, M. et al. One-dimensional flat bands in twisted bilayer germanium selenide. Nat Commun 11, 1124 (2020). https://doi.org/10.1038/s41467-020-14947-0