Fig. 1: Bright and dark exciton complexes in monolayer WS₂.

a Upon irradiation, exciton density follows a Gaussian distribution imprinted by the laser. In the high-density region, the energy of dark excitons increases due to the repulsive interaction. The extra interaction energy drifts dark excitons allowing them to propagate over large areas of the sample and optically recombine far away from the excitation spot. The rainbow ramp represents the energy landscape used in our experiments in which the energy increases linearly due to strain. The energy of bright excitons does not change significantly due to the smaller density and, as a result, they do not drift and their emission is limited to the region of the laser excitation. b Emission spectra of WS₂ at T = 7 K excited with σ⁺ circular polarization and collected with σ⁺ (blue line) and σ⁻ (red line). The top panel shows the chirality of the emission \(\rho=\frac{{I}^{+}-{I}^{-}}{{I}^{+}+{I}^{-}}\), where \({I}^{+}\) and \({I}^{-}\) are the emission intensity of σ⁺ and σ⁻ polarized light, respectively. The peaks of bright and dark exciton complexes are highlighted by vertical dashed lines. The band compositions of the relevant dark exciton species are illustrated in the cartoon in (c–f).