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.
@article{arxiv.1804.10347,
title = {Observation of exciton redshift-blueshift crossover in monolayer WS2},
author = {Edbert J. Sie and Alexander Steinhoff and Christopher Gies and Chun Hung Lui and Qiong Ma and Malte Rosner and Gunnar Schonhoff and Frank Jahnke and Tim O. Wehling and Yi-Hsien Lee and Jing Kong and Pablo Jarillo-Herrero and Nuh Gedik},
journal= {arXiv preprint arXiv:1804.10347},
year = {2018}
}