Strong Coulomb interactions can drive electrons to crystallize into a Wigner lattice. Achieving the bosonic analogue - a crystal of excitons - has remained elusive due to their short lifetimes and weaker interactions. Here, we report the observation of a thermodynamically stable exciton crystal in an excitonic insulator coupled to a moir\'e potential. Using an electron-hole bilayer composed of a monolayer MoSe2 and a WS2/WSe2 moir\'e superlattice, we construct a tunable extended Bose-Hubbard model with electrical control over exciton and charge doping in thermal equilibrium. Optical spectroscopy reveals spontaneous crystallization of long-lived excitons at one exciton filling per three moir\'e sites, evidenced by strong Umklapp scattering peaks in the optical spectrum. Exciton transport measurements further show a pronounced exciton resistance peak at the same filling, consistent with suppressed exciton hopping in a crystalline phase. When doped away from net charge neutrality, this moir\'e electron-hole bilayer can host new correlated insulating phases where dipolar excitonic insulators form on top of the background of a hole Mott insulator or generalized Wigner crystals in the moir\'e superlattice. These findings establish moir\'e excitonic insulators as a versatile platform for realizing correlated crystalline phases of bosons and fermions.
@article{arxiv.2601.19603,
title = {Observation of an exciton crystal in a moir\'e excitonic insulator},
author = {Ruishi Qi and Qize Li and Haleem Kim and Jiahui Nie and Zuocheng Zhang and Ruichen Xia and Zhiyuan Cui and Jianghan Xiao and Takashi Taniguchi and Kenji Watanabe and Michael F. Crommie and Feng Wang},
journal= {arXiv preprint arXiv:2601.19603},
year = {2026}
}