Ultrafast Band Structure Control of a Two-Dimensional Heterostructure

TL;DR

This study demonstrates ultrafast control of the electronic band structure in a 2D heterostructure of MoS₂ on graphene, revealing significant, rapid band gap renormalization due to persistent electronic interactions despite environmental screening.

Contribution

It introduces a time-resolved photoemission technique to directly observe transient band structure changes in 2D heterostructures, highlighting their tunability.

Findings

Band gap of MoS₂ reduced by up to 400 meV after optical excitation

Persistent electronic interactions despite environmental screening

Femtosecond timescale of band structure evolution

Abstract

The electronic structure of two-dimensional (2D) semiconductors can be significantly altered by screening effects, either from free charge carriers in the material itself, or by environmental screening from the surrounding medium. The physical properties of 2D semiconductors placed in a heterostructure with other 2D materials are therefore governed by a complex interplay of both intra- and inter-layer interactions. Here, using time- and angle-resolved photoemission, we are able to isolate both the layer-resolved band structure and, more importantly, the transient band structure evolution of a model 2D heterostructure formed of a single layer of MoS$_2$ on graphene. Our results reveal a pronounced renormalization of the quasiparticle gap of the MoS$_2$ layer. Following optical excitation, the band gap is reduced by up to $\sim\!$400 meV on femtosecond timescales due to a persistence of strong electronic interactions despite the environmental screening by the $n$-doped graphene. This points to a large degree of tuneability of both the electronic structure and electron dynamics for 2D semiconductors embedded in a van der Waals-bonded heterostructure.