Ultrafast exciton many-body interaction in WS₂ single crystal

Transition metal dichalcogenides (TMDCs) have become forefront in research field due to their outstanding properties like strong light-matter interaction, large exciton binding energy in monolayer (ML) limit, etc. The optical properties in these materials are controlled by the robust excitons. Therefore, a microscopic understanding of exciton interactions and recombination in TMDCs plays an integral role in designing optoelectronic devices. Though the exciton dynamics is studied extensively in atomically thin ML, few layers and heterostructure, such studies are scarce in single crystals. Here, by ultrafast transient differential reflectance spectroscopy, we studied exciton many-body interaction in WS₂ single crystal. Time-resolved studies reveal strongly correlated exciton interaction of A, B and C excitons and their associated transient stark blueshift and excitonic broadening. We observe fluence-dependent photoinduced absorption between A and B exciton, attributed to bandgap renormalization and C exciton is detected only at higher fluence. Furthermore, A and B exciton bleaches are decaying biexponentially and show unusually long decay at higher fluence, which prompts potential application of TMDCs in optoelectronics.