Direct observation of giant binding energy modulation of exciton complexes in monolayer MoSe$_2$

TL;DR

This study demonstrates the significant modulation of exciton binding energies in monolayer MoSe$_2$ through dielectric environment changes, revealing a complex interplay with bandgap renormalization and potential for novel optoelectronic devices.

Contribution

It provides the first direct experimental evidence of giant binding energy modulation of exciton complexes in monolayer TMDs due to dielectric screening effects.

Findings

Exciton binding energy can be modulated by over 58% in monolayer MoSe$_2$.

The 1s exciton peak remains unchanged despite dielectric screening.

Bandgap renormalization reduces the quasi-particle bandgap by approximately 248 meV.

Abstract

Screening due to surrounding dielectric medium reshapes the electron-hole interaction potential and plays a pivotal role in deciding the binding energies of strongly bound exciton complexes in quantum confined monolayers of transition metal dichalcogenides (TMDs). However, owing to strong quasi-particle bandgap renormalization in such systems, a direct quantification of estimated shifts in binding energy in different dielectric media remains elusive using optical studies. In this work, by changing the dielectric environment, we show a conspicuous photoluminescence (PL) peak shift at low temperature for higher energy excitons (2s, 3s, 4s, 5s) in monolayer MoSe$_2$, while the 1s exciton peak position remains unaltered - a direct evidence of varying compensation between screening induced exciton binding energy modulation and quasi-particle bandgap renormalization. The estimated modulation of binding energy for the 1s exciton is found to be 58.6% (70.5% for 2s, 78.9% for 3s, 85% for 4s) by coating an Al$_2$O$_3$ layer on top, while the corresponding reduction in quasi-particle bandgap is estimated to be 248 meV. Such a direct evidence of large tunability of the binding energy of exciton complexes as well as the bandgap in monolayer TMDs holds promise of novel device applications.