Non-linear diffusion of negatively charged excitons in WSe2 monolayer

TL;DR

This study explores the non-linear, negative diffusion behavior of negatively charged excitons in WSe2 monolayers, revealing complex dynamics and proposing a model with hot and cold trion populations.

Contribution

It provides the first detailed analysis of non-linear diffusion of trions in WSe2 monolayers, introducing a phenomenological model with two distinct excitonic populations.

Findings

Identification of non-linear, negative diffusion of trions

Observation of bimolecular formation of excitons

Proposal of a two-population diffusion model

Abstract

We investigate the diffusion process of negatively charged excitons (trions) in WSe2 transition metal dichalcogenide monolayer. We measure time-resolved photoluminescence spatial profiles of these excitonic complexes which exhibit a non-linear diffusion process with an effective negative diffusion behavior. Specifically, we examine the dynamics of the two negatively charged bright excitons (intervalley and intravalley trion) as well as the dark trion. The time evolution allows us to identify the interplay of different excitonic species: the trionic species appear after the neutral excitonic ones, consistent with a bimolecular formation mechanism. Using the experimental observations, we propose a phenomenological model suggesting the coexistence of two populations: a first one exhibiting a fast and efficient diffusion mechanism and a second one with a slower dynamics and a less efficient diffusion process. These two contributions could be attributed to hot and cold trion populations.