Interactions between Fermi polarons in monolayer WS2

• Published in: Nature communications Vol. 13; no. 1; p. 6164
• Main Authors: Muir, Jack B., Levinsen, Jesper, Earl, Stuart K., Conway, Mitchell A., Cole, Jared H., Wurdack, Matthias, Mishra, Rishabh, Ing, David J., Estrecho, Eliezer, Lu, Yuerui, Efimkin, Dmitry K., Tollerud, Jonathan O., Ostrovskaya, Elena A., Parish, Meera M., Davis, Jeffrey A.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 18.10.2022; Nature Publishing Group; Nature Portfolio
• Subjects: 639/766/119/1000/1018; 639/766/119/995; Binding energy; Doping; Electron gas; Electrons; Elementary excitations; Excitons; Fine structure; Humanities and Social Sciences; Impurities; Monolayers; multidisciplinary; Polarons; Science; Science (multidisciplinary); Spectroscopy; Spectrum analysis; Superconductivity; Superlattices; Thermodynamics; Ultrastructure; Valleys
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-022-33811-x

Interactions between quasiparticles are of fundamental importance and ultimately determine the macroscopic properties of quantum matter. A famous example is the phenomenon of superconductivity, which arises from attractive electron-electron interactions that are mediated by phonons or even other more exotic fluctuations in the material. Here we introduce mobile exciton impurities into a two-dimensional electron gas and investigate the interactions between the resulting Fermi polaron quasiparticles. We employ multi-dimensional coherent spectroscopy on monolayer WS 2 , which provides an ideal platform for determining the nature of polaron-polaron interactions due to the underlying trion fine structure and the valley specific optical selection rules. At low electron doping densities, we find that the dominant interactions are between polaron states that are dressed by the same Fermi sea. In the absence of bound polaron pairs (bipolarons), we show using a minimal microscopic model that these interactions originate from a phase-space filling effect, where excitons compete for the same electrons. We furthermore reveal the existence of a bipolaron bound state with remarkably large binding energy, involving excitons in different valleys cooperatively bound to the same electron. Our work lays the foundation for probing and understanding strong electron correlation effects in two-dimensional layered structures such as moiré superlattices. Here, the authors investigate the interactions between Fermi polarons in monolayer WS 2 by multi-dimensional coherent spectroscopy, and find that, at low electron doping densities, the dominant interactions are between polaron states that are dressed by the same Fermi sea. They also observe a bipolaron bound state with large binding energy, involving excitons in different valleys cooperatively bound to the same electron.