Polariton transport in 2D semiconductors: Phonon-mediated transitions between ballistic, superdiffusive and exciton-limited regimes

TL;DR

This paper explores how phonons influence polariton transport in 2D semiconductors, revealing three regimes from ballistic to diffusive, which aids in designing advanced optoelectronic devices.

Contribution

It provides a microscopic understanding of phonon effects on polariton transport regimes in 2D materials, including the crossover mechanisms.

Findings

Identified three distinct transport regimes: ballistic, superdiffusive, and exciton-limited.

Demonstrated phonon-induced velocity renormalization affects initial transport.

Revealed superdiffusive behavior with enhanced diffusion during transient regime.

Abstract

Exciton transport in 2D semiconductors holds promise for room-temperature, ultra-compact optoelectronic devices, but it is limited by short propagation distances. Hybridization of excitons with cavity photons to form exciton-polaritons can enhance the propagation by orders of magnitude, enabling a coherent, ballistic transport. However, a microscopic understanding of the role of phonons is still lacking, particularly regarding their influence on the crossover from the ballistic to the diffusive polariton transport regime. Here, we investigate the spatiotemporal polariton dynamics in \ce{MoSe2} monolayers at moderate to high temperatures, explicitly including the phonon-mediated coupling to the intervalley exciton reservoir. We identify three distinct transport regimes: (i) an initial sub-ps ballistic-like regime characterized by a phonon-induced velocity renormalization, (ii) a transient, few-ps superdiffusive regime characterized by strongly enhanced diffusion, and (iii) a slower, exciton-limited diffusion following thermalization. The gained microscopic insights will trigger and guide future experimental studies on the phonon-mediated polariton transport in atomically thin semiconductors.