Dispersion of the nonlinear susceptibility of MoS2 and WS2 from second-harmonic scattering spectroscopy

Dispersion of the absolute second-order susceptibility of both $\mathrm{Mo}{\mathrm{S}}_{2}$ and $\mathrm{W}{\mathrm{S}}_{2}$ is assessed on a wide spectral excitation range (710--1300 nm) by using second-harmonic scattering spectroscopy (SHS). SHS is an accurate ensemble measurement here applied on well-dispersed suspensions of monodisperse liquid-exfoliated nanosheets showing a high monolayer content. The as-derived, high susceptibility values shed light on the discrepancies between available literature values while evidencing resonances associated with the main excitonic transitions.