Dynamic screening of quasiparticles in WS$_2$ monolayers

TL;DR

This study investigates how quasiparticle screening affects exciton dynamics in monolayer WS$_2$, revealing photon energy-dependent shifts and distinct roles of excitons and free carriers in band gap renormalization.

Contribution

It introduces a phenomenological model to differentiate the effects of excitons and free carriers on quasiparticle screening in WS$_2$ monolayers.

Findings

Photon energy influences exciton blue and red-shifts.

Excitons and free carriers have different impacts on band gap renormalization.

The model isolates contributions of excitons and carriers to screening.

Abstract

We unravel the influence of quasiparticle screening in the non-equilibrium exciton dynamics of monolayer WS$_2$. We report pump photon energy-dependent exciton blue and red-shifts from time-resolved-reflectance contrast measurements. Based on a phenomenological model, we isolate the effective impact of excitons and free carriers on the renormalization of the quasi-free particle band gap, exciton binding energy and linewidth broadening. By this, our work does not only provide a comprehensive picture of the competing phenomena governing the exciton dynamics in WS$_2$ upon photoexcitation, but also demonstrates that exciton and carrier contributions to dynamic screening of the Coulomb interaction differ significantly.