Frequency-dependent substrate screening of excitons in atomically thin transition metal dichalcogenide semiconductors

TL;DR

This paper explores how dynamical substrate screening, especially via plasmons in doped substrates, influences exciton properties in atomically thin TMDC semiconductors, revealing tunable optical behaviors and stable excitons.

Contribution

It provides a theoretical analysis of dynamical screening effects in TMDCs due to doped substrates, highlighting the role of plasmons in exciton manipulation.

Findings

Dynamical screening leads to more spectrally stable excitons than static models predict.

Substrate doping density nontrivially affects the single-particle band gap.

Plasmons can be used to tune excitonic properties on the nanoscale.

Abstract

Atomically thin layers of transition metal dichalcogenides (TMDCs) exhibit exceptionally strong Coulomb interaction between charge carriers due to the two-dimensional carrier confinement in connection with weak dielectric screening. The van der Waals nature of interlayer coupling makes it easy to integrate TMDC layers into heterostructures with different dielectric or metallic substrates. This allows to tailor electronic and optical properties of these materials, as Coulomb interaction inside atomically thin layers is very susceptible to screening by the environment. Here we theoretically investigate dynamical screening effects in TMDCs due to bulk substrates doped with carriers over a large density range, thereby offering three-dimensional plasmons as tunable degree of freedom. We report a wide compensation of renormalization effects leading to a spectrally more stable exciton than predicted for static substrate screening, even if plasmons and excitons are in resonance. We also find a nontrivial dependence of the single-particle band gap on substrate doping density due to dynamical screening. Our investigation provides microscopic insight into the mechanisms that allow for manipulations of TMDC excitons by means of arbitrary plasmonic environments on the nanoscale.