Fig. 4: Highly unidirectional and narrow-linewidth exciton emission from monolayer WSe₂ when coupled with the ultrahigh-Q meta-resonator at room temperature.

a Left, Energy-momentum photoluminescence (PL) spectra of monolayer WSe₂ in the unpatterned structure. Pumped by a 532 nm 0.555 kW/cm² CW laser. The broad full-width-at-half-maximum (FWHM) linewidths in far-field emission angle (\({\varGamma }_{\theta }\)) and spectral wavelength (\({\varGamma }_{\lambda }\)) are highlighted; Right, Energy-momentum reflectance spectra of the WSe₂-metasurface hybrid system, where P = 480 nm and L = 70 nm. b Narrowing the WSe₂ PL in both spectral and angular dimensions. Top, Schematics of monolayer WSe₂ in the unpatterned structure and patterned meta-resonator on a fused silica substrate (no Si wafer), respectively. The same device is measured before and after PMMA patterning. Bottom, Comparison of WSe₂ PL linewidths before and after patterning, in both spectral (Left) and angular (Right) dimensions. c–e Extracted emission properties of the WSe₂-metasurface hybrid from the energy-momentum PL spectra (Supplementary Fig. S7) as a function of pump power density (logarithmic scale): (c) spectral linewidth, FWHM \({\varGamma }_{\lambda }\), (d) angular linewidth, FWHM \({\varGamma }_{\theta }\), and (e) integrated PL counts (logarithmic scale) at sin \(\theta\) = 0.012 (orange dots) and sin \(\theta\) = 0 (black dots), respectively. The error bars in (c, d) are determined by spectra fittings (see Methods). The integrated PL in (e) were measured by first increasing the laser power and then decreasing it by 3 times. The error bar shows the standard deviation.