A perturbative approach to the polaron shift of excitons in transition metal dichalcogeniedes

TL;DR

This paper presents a perturbative theoretical approach to understanding how phonons influence the excitonic resonance position in two-dimensional transition metal dichalcogenides, specifically applied to WS₂, with results matching experimental data.

Contribution

The paper introduces a simple two-ingredient perturbative model combining phonon effects on exciton resonance and energy gap shifts, accurately predicting temperature-dependent spectral shifts.

Findings

Excellent agreement with experimental peak shifts

Perturbation theory effectively models phonon effects

Huang-Rhys model captures energy gap modifications

Abstract

In this paper we study the phonon's effect on the position of the 1s excitonic resonance of the fundamental absorption transition line in two-dimensional transition metal dichalcogenides. We apply our theory to WS$_{2}$a two-dimensional material where the shift in absorption peak position has been measured as a function of temperature. The theory is composed of two ingredients only: i) the effect of longitudinal optical phonons on the absorption peak position, which we describe with second order perturbation theory; ii) the effect of phonons on the value of the single particle energy gap, which we describe with the Huang Rhys model. Our results show an excellent agreement with the experimentally measured shift of the absorption peak with the temperature.