The exciton–polaritonic states are generated by the strong interaction between photons and excitons in confined nanocavities. To achieve strong coupling between excitons in TMDCs and optical modes in cavities is quite challenging due to fabrication issues, modal and material dispersion in the cavity, and the weak confinement of the optical field. Hence, investigation of new photonic structures to achieve strong coupling in TMDCs materials is necessary to develop polariton-based devices. Here, we report the observation of the strong coupling between an anapole mode in a slotted silicon nanodisk and an exciton in a WSe2 monolayer, leading to the creation of anapole–exciton polaritons. Furthermore, we have also demonstrated a strong anapole–plasmon and anapole–plasmon–exciton coupling in Si–Ag, and Si–Ag–WSe2 heterostructures, respectively. The observed polaritonic hybrid states have a large Rabi splitting (159 meV) accompanied by high localized field enhancement (157 times increase) in the near field and at a normal incident angle, suggesting a crucial step toward the creation of exciton–polariton nanodevices.

Transition-metal dichalcogenides (TMDCs) monolayers have been considered a perfect platform for realizing exciton-polariton at room temperature due to their direct bandgap and large binding energy of exciton. It is well established that strong coupling depends on the field enhancement induced by optical nanocavity with a high-quality factor (Q-factor). In this work, the enhanced strong coupling between the exciton of TMDC monolayer and the cavity resonance based on a symmetry protected magnetic dipole (MD) bound state in the continuum (BIC) and electric toroidal dipole (TD) BIC is demonstrated. It is found that strong coupling can be realized between the exciton in a TMDC monolayer and quasi-BIC (QBIC) by varying the incidence angle, period of the grating, the width of the slit, and the position of the slit for symmetry protected BIC. Besides, strong coupling between exciton and TD BIC is also demonstrated by integrating a WSe 2 monolayer onto a compound grating. It is found that Rabi-splitting strongly depends on the location of TMDC monolayer, Q-factor of the resonator, and the thickness of the structure. By carefully adjusting these three critical parameters, Rabi-splitting can be up to 38 (1L-WSe 2 ), 65 (1L-WS 2 ), 40 (1L-MoSe 2 ), and 60 meV(1L-MoS 2 ).

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