Fig. 1: Strong exciton-photon coupling and van der Waals materials.

a Schematic diagram of a cavity system with a single two-level active material embedded between two high-reflective mirrors. The parameters involved in the strong interaction regimes are the resonance frequency \({\omega }_{c}\) of the cavity mode, the resonance \({\omega }_{X}\) of optical gain materials, the light-matter interaction strength g, and the lifetime of the cavity photon \({\gamma }_{c}^{-1}\) and exciton \({\gamma }_{X}^{-1}\). b A typical exciton-polariton dispersion of a strongly coupled excitons and cavity mode. c The Brillouin zone and band structure at the K points. d The reflectance contrast derivative (\(\varDelta R/R\)) of a WS₂ monolayer. The spectrum shows the ground state and the higher Rydberg-series states (2 s, 3 s, 4 s, 5 s…) of A exciton. e Schematic of a typical heterostructure formed by two different TMDs with twist angle \(\theta\) in momentum space, resulting in an intralayer and interlayer exciton at the K/K’ valley. c Reprinted with permission from ref. ²⁷ [American Physical Society]. d Adapted with permission from ref. ³² [American Physical Society]. e Reprinted with permission from ref. ²⁶ [Springer Nature Limited]