Controlled dynamic screening of excitonic complexes in 2D semiconductors

TL;DR

This study combines theory and experiments to understand how excitons in 2D semiconductors are dynamically screened by their environment, affecting their optical properties.

Contribution

It introduces an analytical model for dynamic screening of excitons and experimentally verifies it in monolayer WS2 with various screening environments.

Findings

Screening shifts excitonic peaks in photoluminescence spectra.

Model accurately predicts environment-dependent exciton energy shifts.

Dynamic screening depends on exciton symmetry and transition energies.

Abstract

We report a combined theoretical/experimental study of dynamic screening of excitons in media with frequency-dependent dielectric functions. We develop an analytical model showing that interparticle interactions in an exciton are screened in the range of frequencies from zero to the characteristic binding energy depending on the symmetries and transition energies of that exciton. The problem of the dynamic screening is then reduced to simply solving the Schrodinger equation with an effectively frequency-independent potential. Quantitative predictions of the model are experimentally verified using a test system: neutral, charged and defect-bound excitons in two-dimensional monolayer WS2, screened by metallic, liquid, and semiconducting environments. The screening-induced shifts of the excitonic peaks in photoluminescence spectra are in good agreement with our model.