Steady-state nonlinear optical response of excitons in monolayer MoSe$_2$

TL;DR

This paper investigates the steady-state nonlinear optical response of excitons in monolayer MoSe$_2$, revealing polarization-dependent signals and matching experimental results with a detailed theoretical model.

Contribution

It provides the first comprehensive analysis of steady-state nonlinear excitonic responses in monolayer MoSe$_2$, including a theoretical model that accurately reproduces experimental spectra.

Findings

Differential transmission signals depend on polarization.

Two-exciton correlations dominate the nonlinear response.

No strong biexciton binding observed.

Abstract

Monolayer transition metal dichalcogenide (TMD) semiconductors such as MoSe$_2$ host strongly bound excitons which are known to exhibit a strong resonant third-order nonlinear response. Although there have been numerous studies of the ultrafast nonlinear response of monolayer TMDs, a study of the steady-state nonlinear response is lacking. We report a comprehensive study of the steady-state two-color nonlinear response of excitons in hBN-encapsulated monolayer MoSe$_2$ at 7 K. We observe differential transmission (DT) signals associated with the neutral and charged exciton species, which is strongly dependent on the polarization of the pump and probe. Our results are compared to a theoretical model based on a T-matrix formulation for exciton-exciton, exciton-trion, and trion-trion correlations. The parameters are chosen such that the theory accurately reproduces the experimental DT spectrum, which is found to be dominated by two-exciton correlations without strong biexciton binding, exciton-trion attractive interactions, and strong spin mixing through incoherent relaxation.