Fig. 4. Screening length of excitons in heterostructure and the effect of hybridization on the exciton resonance in WSe₂ trilayer.

a, b Near-field images of the normalized amplitude $s_5\left(\omega \right)/s_5\left(h-\mathrm{BN}\right)$ and phase ${\phi }_5\left(\omega \right)-{\phi }_5\left(h-\mathrm{BN}\right)$. The images in the left and right panels were taken at 1.68 eV (around the monolayer WSe₂ exciton resonance energy) and 1.57 eV (around monolayer MoSe₂ exciton resonance energy), respectively. The boundaries of the materials are displayed with dash lines. The scale bars indicate 400 nm. c Line profiles of the normalized amplitude and phase across the monolayer and heterobilayer along the black lines in the right panels in (a and b). d, e Normalized scattering amplitude $s_5\left(\omega \right)/s_5\left(h-\mathrm{BN}\right)$ and phase ${\phi }_5\left(\omega \right)$ spectra for WSe₂ trilayer (data points). The near-field data are fitted by the point dipole model (solid curves). The vertical blue dashed and solid lines in e are used to mark the exciton energies of WSe₂ monolayer and WSe₂ trilayer extracted from the point dipole model, respectively.