Microscopic modelling of exciton-polariton diffusion coefficients in atomically thin semiconductors

TL;DR

This paper models exciton-polariton diffusion in atomically thin semiconductors, predicting significant increases in diffusion coefficients due to strong light-matter coupling effects, enhancing understanding of polariton transport.

Contribution

It introduces a microscopic model combining exciton density matrix and Hopfield approach to quantify polariton diffusion in 2D semiconductors under strong coupling.

Findings

Diffusion coefficients increase by 2-3 orders of magnitude in strong coupling.

Polariton group velocity is significantly larger than that of bare excitons.

Polariton-phonon scattering channels are suppressed in the strong coupling regime.

Abstract

In the strong light-matter coupling regime realized e.g. by integrating semiconductors into optical microcavities, polaritons as new hybrid light-matter quasi-particles are formed. The corresponding change in the dispersion relation has a large impact on optics, dynamics and transport behaviour of semiconductors. In this work, we investigate the strong-coupling regime in hBN-encapsulated MoSe$_2$ monolayers focusing on exciton-polariton diffusion. Applying a microscopic approach based on the exciton density matrix formalism combined with the Hopfield approach, we predict a drastic increase of the diffusion coefficients by two to three orders of magnitude in the strong coupling regime. We explain this behaviour by the much larger polariton group velocity and suppressed polariton-phonon scattering channels with respect to the case of bare excitons. Our study contributes to a better microscopic understanding of polariton diffusion in atomically thin semiconductors.