Influence of the effective layer thickness on the groundstate and excitonic properties of transition-metal dichalcogenide systems

TL;DR

This paper presents a comprehensive theoretical approach to analyze how the effective layer thickness influences the groundstate and excitonic optical properties of transition-metal dichalcogenides, aligning well with experimental observations.

Contribution

It introduces a self-consistent scheme combining dielectric modeling, gap equations, and the Dirac-Wannier equation, incorporating an effective thickness parameter for multilayer TMD systems.

Findings

Finite size effects significantly modify optical spectra.

The model reproduces non hydrogenic excitonic features.

Interlayer excitons are predicted in multilayer systems.

Abstract

A self-consistent scheme for the calculations of the interacting groundstate and the near bandgap optical spectra of mono- and multilayer transition-metal-dichalcogenide systems is presented. The approach combines a dielectric model for the Coulomb interaction potential in a multilayer environment, gap equations for the renormalized groundstate, and the Dirac-Wannier-equation to determine the excitonic properties. To account for the extension of the individual monolayers perpendicular to their basic plane, an effective thickness parameter in the Coulomb interaction potential is introduced. Numerical evaluations for the example of MoS$_2$ show that the resulting finite size effects lead to significant modifications in the optical spectra, reproducing the experimentally observed non hydrogenic features of the excitonic resonance series. Applying the theory for multi-layer configurations, a consistent description of the near bandgap optical properties is obtained all the way from monolayer to bulk. In addition to the well-known in-plane excitons, also interlayer excitons occur in multilayer systems suggesting a reinterpretation of experimental results obtained for bulk material.