Emergence of composite 6-particle "hexciton" states in WS₂ and MoSe₂ monolayers

When doped with a high density of mobile charge carriers, the monolayer transition-metal dichalcogenide (TMD) semiconductors can host novel types of composite many-particle exciton states that do not exist in conventional semiconductors. Such multi-particle bound states arise when a photoexcited electron-hole pair couples to not just a single Fermi sea that is quantum-mechanically distinguishable (as for the case of conventional charged excitons or trions), but rather couples simultaneously to multiple Fermi seas, each having distinct spin and valley quantum numbers. Composite six-particle "hexciton" states were recently identified in electron doped WSe₂ monolayers [1], but under suitable conditions they should also form in other members of the monolayer TMD family. Here we present spectroscopic evidence for the emergence of many-body hexcitons in charge-tunable WS₂ monolayers (where they form at the A-exciton resonance) and MoSe₂ monolayers (where they form at the B-exciton). [1] D. Van Tuan, S.F. Shi, X. Xu, S.A. Crooker, & H. Dery, Six-Body and Eight-Body Exciton States in Monolayer WSe₂, Phys. Rev. Lett. 129, 076801 (2022).