Strong-Coupling of Hybrid Quasiparticles in Excitonic-Dielectric Gratings*

Tightly bound exciton states in van der Waals semiconductors such as MX₂ (M= Mo, W; X= S, Se) are promising for optoelectronic applications. However, to-date, strong light-exciton interaction and control of excited states in them has been limited to monolayer samples with external optical cavities. Here, we demonstrate that nanostructured multilayer WS₂ provides an ideal cavity-less and exposed surface platform for exciton-photonics where the WS₂ serves the role of both the cavity and the excitonic medium. We show that by patterning sub-15 nm thick WS₂ into 300 nm wide resonators an avoided crossing of excitons and photon-polaritons with interaction potentials exceeding 410 meV can be engineered with precision. We further observe that inherently strong TMDC exciton absorption may be completely suppressed due to excitation of hybrid photon-exciton states and their interference. By modifying the system with dielectric spacers, we observe a rich platform for coupling and field confinement with bulk and monolayer TMDCs. Our work paves the way to a new class of integrated exciton optoelectronic nano-devices and their applications in light generation and manipulation.