Probing the nonlinear response of strongly coupled plasmon-WSe₂ system

Two-dimentional transition metal dichalcogenides (TMDs) have recently emerged as a class of material that shows a great potential for strong light-matter interaction at the nanoscale. Signatures of strong coupling, such as Rabi-splitting in the linear optical spectra, have been observed by placing TMDs in optical nanocavities. Typically, plasmonic nanocavities and nanostructures are used to reach the appropriate parameters for the observation of strong coupling regime. However, most studies utilize dark field (DF) scattering experiments rather than photoluminescence (PL) for the demonstration of strong coupling phenomena, whereas the observation of PL splitting in this system has rarely been reported. Thus, more convincing evidences of strong coupling are still needed.
We have successfully assembled gold nanoparticles and TMD materials (WSe₂) to investigate the strong light-matter interaction in TMDs. Interestingly, our simulation based on a two-oscillator toy model predicts that second harmonic generation will show a pronounced spectral splitting in this regime. Thus, we suggest that probing of these systems in the nonlinear regime may give clearer evidence of strong coupling that could not be observed in the linear measurements.