Fig. 1.

Optical signature of single and multilayer WSe₂ embedded in plasmonic nanocavities. a, b Schematic of nanoparticle-on-mirror cavity encapsulating WSe₂ flakes for N _L = 1,12. c, d Dark-field scattering of individual NPoMs showing single-plasmon peak for N _L = 1 WSe₂, but a mode splitting due to strong coupling for multilayer N _L = 12 reproduced by FDTD simulations (dashed line). e, f Simulated field distributions E _x,z for two plasmon-coupled modes (s₀₂, s₁₁) at λ = 780 nm with high refractive index material (dashed) in the 10 nm gap (n = 2.8). Angles of incidence 55° (left) and 0° (right); red-blue colour-scale shows field enhancements of $\pm 30∣E_0∣$