Enhanced strong coupling of WSe₂monolayer by Bound State in the continuum

Due to the large binding energy and direct bandgap, transition-metal dichalcogenides (TMDCs) monolayers have been considered a perfect platform for realising strong coupling at room temperature. It is well established that the quality factor (Q-factor) plays a crucial role in enhancing strong coupling. In this work, we demonstrate the improved strong coupling between the exciton of the WSe2 monolayer and the high Q cavity resonance based on symmetry protected magnetic dipole (MD) bound state in the continuum (BIC). We have found that the Rabi-splitting of the strongly coupled system could be largely enhanced by adjusting the location of the TMDC monolayer, increasing the Q-factor, and reducing the grating thickness. After carefully adjusting the three critical parameters, a Rabi-splitting as high as 38 meV was achieved limited by the oscillator strength of the WSe2 monolayer. Our system could be considered an excellent platform to realise ultra-thin polaritonic devices.