Fig. 2: Room-temperature strong coupling in hBN/WS2/hBN vdW-HMs.
From: Atomic-layer assembly of ultrathin optical cavities in van der Waals heterostructure metasurfaces
a, Optical image of the vdW heterostructure. The WS2 monolayer (black outline) is encapsulated between a bottom hBN layer (light-pink area) and a top hBN (purple area) using a multistep heterostructure fabrication process (top panel). Right panel: optical image of the final vdW-HM sample after lithography-based nanofabrication. The bright square is the unstructured reference heterostructure sample. b, Schematic and side view of a single qBIC metasurface unit cell, composed of hBN/WS2/hBN layers with a total height of 125 nm. Inset: geometry of the metasurface unit cell, where px = py is the lattice periodicity, w is the nanorod width, L0 is the base rod length and ΔL is the asymmetry factor. c, PL spectra of the reference vdW heterostructure and a positively detuned vdW-HM showing negligible changes in the PL emission spectra, confirming the preservation of monolayer quality after the fabrication step. d, Transmittance of the reference WS2 heterostructure sample, exhibiting the excitonic peak at 2 eV (multiplied 15 times), and that of the resonant qBIC metasurface, exhibiting a clear splitting at the corresponding exciton energy. e, Derivative of the transmittance (dT/dE) for the full set of optical metasurfaces for the sample shown in a, fitted with the coupled harmonic oscillator model described in the Methods. Inset: selected derivative trace for vdW-HM at close-to-zero detuning (in black) and negatively and positively detuned metasurfaces as comparison (in grey). f, PL emission as a function of scaling factor S and relative qBIC–exciton detuning δ. The white dots represent the PL peak maxima, and the data are fitted from the same coupled harmonic oscillator as that in e. g, Normalized WS2 PL spectra from different vdW metasurfaces with increasing scaling factor (bottom to top).
