Observation of an exciton crystal in a moir\'e excitonic insulator

Ruishi Qi; Qize Li; Haleem Kim; Jiahui Nie; Zuocheng Zhang; Ruichen Xia; Zhiyuan Cui; Jianghan Xiao; Takashi Taniguchi; Kenji Watanabe; Michael F. Crommie; Feng Wang

arXiv · 2601.19603

Observation of an exciton crystal in a moir\'e excitonic insulator

Ruishi Qi·Qize Li·Haleem Kim·Jiahui Nie·Zuocheng Zhang·Ruichen Xia·Zhiyuan Cui·Jianghan Xiao·Takashi Taniguchi·Kenji Watanabe·Michael F. Crommie·Feng Wang

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Abstract

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.

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Ruishi Qi, Qize Li, Haleem Kim, Jiahui Nie, Zuocheng Zhang, Ruichen Xia, Zhiyuan Cui, Jianghan Xiao, Takashi Taniguchi, Kenji Watanabe, Michael F. Crommie, Feng Wang. 2026-01-27. Observation of an exciton crystal in a moir\'e excitonic insulator. https://arxiv.org/abs/2601.19603

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