Muir, Jack BLevinsen, JesperEarl, Stuart KConway, Mitchell ACole, Jared HWurdack, MatthiasMishra, RishabhIng, David J.Estrecho, EliezerLu, YueruiEfimkin, Dmitry K.Tollerud, Jonathan OOstrovskaya, ElenaParish, Meera M.Davis , Jeffrey A.2026-06-172026-06-17Bibtex:muir2022excitonORCID:/0000-0001-6131-3906/work/217688989ORCID:/0000-0003-0523-6533/work/217692377https://hdl.handle.net/1885/733811535Interactions 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 WS2, 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.This work was supported by the Australian Research Council Center of Excellence in Future Low-Energy Electronics Technologies (CE170100039). M.M.P. and J.L. were supported through the Australian Research Council Future Fellowships FT200100619 and FT160100244, respectively. J.H.C. and D.J.I. also acknowledge the support of the Australian National Computational Infrastructure (NCI) and the ARC Centre of Excellence in Exciton Science (CE170100026). Y.L. acknowledges the support of ARC Centre of Excellence in Quantum Computation and Communication Technology (CE170100012). E.E. was supported through the Australian Research Council Discovery Early Career Research Award DE220100712.222022-10-1810.1038/s41467-022-33811-x