Photonic spin-controlled self-hybridized exciton-polaritons in WS2 metasurfaces driven by chiral quasibound states in the continuum

Bulk transition metal dichalcogenides (TMDs) have found widespread applications on nanophotonics, condensed matter physics, and quantum optics, due to their high refractive index and stable excitonic response at room temperature. In this paper, based on the finite-element method simulations, we demonstrate that the high refractive index enables the fabrication of bulk $\mathrm{W}{\mathrm{S}}₂$ into high-quality-factor metasurfaces that support chiral quasibound states in the continuum (Q-BICs). Interestingly, the Q-BIC resonance can in turn hybridize with excitons in the $\mathrm{W}{\mathrm{S}}₂$ metasurface itself. The self-hybridized exciton-polaritons, induced by the strong coupling between a Q-BIC and excitons, exhibit a typical anticrossing behavior with the Rabi splitting up to 136.5 meV. Such remarkable anticrossing behavior is also well elucidated by the coupled oscillator model. Intriguingly, we numerically verify that the self-hybridized exciton-polaritons are photonic spin-controlled, attributed to the chiral Q-BIC with the circular dichroism approaching 0.91. Therefore, we can control the exciton-photon interaction by simply changing the helicity of incident light. We believe that the outstanding self-hybridized exciton-polaritons in a $\mathrm{W}{\mathrm{S}}₂$ metasurface itself, without external microcavities, could pave the way for large-scale, low-cost integrated polaritonic devices at room temperature. Additionally, the chiral Q-BIC will enrich the toolbox for engineering exciton-photon interactions in bulk TMDs and other semiconductors. The photonic spin-controlled self-hybridized exciton-polaritons would find utility in ultrafast all-optical switches, modulators, chiral light-emitting devices, and valleytronic devices.