Fig. 3: Angle-resolved spectroscopy of vdW-HMs.

a, Numerical results of RCWA simulations of an hBN vdW heterostructure without (negative wavevectors) and with (positive wavevectors) an embedded WS₂ monolayer, where the diffraction order (±1, 0) is shown. In the presence of the monolayer, the dispersion is fitted using the model described in the Methods, with the resulting polariton branches depicted as the dashed white lines. The solid, flat line represents the WS₂ exciton (X) resonance. b, Experimental back-focal-plane imaging of the reflectance from a vdW metasurface with detuning δ = 96 meV. The dispersion is overlaid with the calculated exciton–polariton branches energies (dashed white lines; Methods). c, Reflectance spectrum extracted from the data in b at k_x = 0.09, exhibiting splitting at the corresponding exciton energy (grey-shaded area). d, RCWA numerical simulations of the reflectance from the vdW heterostructure, showing good agreement with the experimental results, and underscoring the effect of the diffraction orders. e, Angular dispersion of the WS₂ PL emission from different vdW-HMs with different detuning values (from left to right: 96 meV, –55 meV and –94 meV). For negatively detuned cavities, the maximum of the PL emission is observed at k_x = 0, corresponding to the qBIC-coupled lower polariton branch.