Many-body interactions and exciton complexes in a layered semiconductor*

Due to their heavy carrier mass and gate tunability, two-dimensional semiconductors are an exciting platform to study the interplay between many-body effects and exciton physics. In particular, the family of III-VI metal monochalcogenides stems out due to its attractive optical properties and flat valence band dispersion. The influence of such singularity in 2D semiconductors remains largely unexplored, mainly due to difficulties in the fabrication that usually yield non-reproducible results. Here, we employ photoluminescence spectroscopy of charge-tunable excitons in few-layer metal monochalcogenides to probe many-body interactions at the flat band. Furthermore, we provide a reliable marker for the flat band position, to corroborate our interpretation. Our results pave the way for a reproducible and potentially manufacturable device to study the effects of flat-band physics without the need for a twist-angle in the heterostack.