Fast low-power all-optical tunable localized exciton-polaritons in nanostructured van der Waals metamaterials

Exciton-polaritons, which are quasiparticles resulting from the strong coupling of excitons to photons, have strong intrinsic nonlinearities. These quasiparticles are essential for emerging technological applications in polaritonic devices. Here low-power fast-response all-optical tunable localized exciton-polaritons were observed in WS2 flakes. The metamaterial comprised 50-nm-thick WS2 flakes with periodic rectangular nanoholes. This configuration shows a resonance dip in the transmission measured spectrum. A comparison with plasmon and phonon polaritons revealed that the resonance behavior originates from localized exciton-polaritons. Because of the large optical nonlinearity of excitons and polaritons, the transmission ratios at the resonant wavelength could be tuned from 0.18 up to 0.44 under an excitation of 85 MW cm-2 using a 402-nm, 120-fs laser beam. The response time, as determined from the electron indirect interband transition, was 48.7 ps. Moreover, the proposed theoretical design demonstrates the widespread existence of localized exciton-polaritons in the material. This van der Waals semiconductor with localized exciton-polaritons and large all-optical tunability shows promising characteristics for low-power all-optical devices and nanophotonic integrated circuits.