Direct Determination of Band Gap Renormalization in Photo-Excited Monolayer MoS2

TL;DR

This study measures how the quasiparticle bandgap in monolayer MoS2 decreases significantly upon photo-excitation, providing direct experimental quantification of bandgap renormalization using advanced spectroscopy.

Contribution

It presents the first direct measurement of bandgap renormalization in monolayer MoS2 using TR-ARPES, highlighting the importance of carrier density in understanding bandgap changes.

Findings

Eg decreases by up to 360 meV at high excitation densities

Bandgap renormalization depends on carrier density and doping levels

Experimental results align with theoretical predictions when doping is considered

Abstract

A key feature of monolayer semiconductors, such as transition-metal dichalcogenides, is the poorly screened Coulomb potential, which leads to large exciton binding energy (Eb) and strong renormalization of the quasiparticle bandgap (Eg) by carriers. The latter has been difficult to determine due to cancellation in changes of Eb and Eg, resulting in little change in optical transition energy at different carrier densities. Here we quantify bandgap renormalization in macroscopic single crystal MoS2 monolayers on SiO2 using time and angle resolved photoemission spectroscopy (TR-ARPES). At excitation density above the Mott threshold, Eg decreases by as much as 360 meV. We compare the carrier density dependent Eg with previous theoretical calculations and show the necessity of knowing both doping and excitation densities in quantifying the bandgap.