Observation of exciton redshift-blueshift crossover in monolayer WS2

TL;DR

This study observes a unique exciton energy shift behavior in monolayer WS2, revealing a crossover from redshift to blueshift due to exciton interactions, with implications for exciton phases in 2D materials.

Contribution

It provides experimental evidence of exciton interaction crossover in monolayer WS2, supported by modeling, highlighting atom-like behavior of excitons in 2D materials.

Findings

Exciton resonance energy shifts from red to blue with increasing excitation density.

Attraction-repulsion crossover in exciton interactions mimics atomic Lennard-Jones potential.

Potential for realizing liquid and crystalline exciton phases in 2D materials.

Abstract

We report a rare atom-like interaction between excitons in monolayer WS2, measured using ultrafast absorption spectroscopy. At increasing excitation density, the exciton resonance energy exhibits a pronounced redshift followed by an anomalous blueshift. Using both material-realistic computation and phenomenological modeling, we attribute this observation to plasma effects and an attraction-repulsion crossover of the exciton-exciton interaction that mimics the Lennard-Jones potential between atoms. Our experiment demonstrates a strong analogy between excitons and atoms with respect to inter-particle interaction, which holds promise to pursue the predicted liquid and crystalline phases of excitons in two-dimensional materials.