Signatures of Wigner crystal of electrons in a monolayer semiconductor

Tomasz Smoleński (), Pavel E. Dolgirev, Clemens Kuhlenkamp, Alexander Popert, Yuya Shimazaki, Patrick Back, Xiaobo Lu, Martin Kroner, Kenji Watanabe, Takashi Taniguchi, Ilya Esterlis, Eugene Demler () and Ataç Imamoğlu ()
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Tomasz Smoleński: Institute for Quantum Electronics, ETH Zürich
Pavel E. Dolgirev: Harvard University
Clemens Kuhlenkamp: Institute for Quantum Electronics, ETH Zürich
Alexander Popert: Institute for Quantum Electronics, ETH Zürich
Yuya Shimazaki: Institute for Quantum Electronics, ETH Zürich
Patrick Back: Institute for Quantum Electronics, ETH Zürich
Xiaobo Lu: Institute for Quantum Electronics, ETH Zürich
Martin Kroner: Institute for Quantum Electronics, ETH Zürich
Kenji Watanabe: National Institute for Materials Science
Takashi Taniguchi: National Institute for Materials Science
Ilya Esterlis: Harvard University
Eugene Demler: Harvard University
Ataç Imamoğlu: Institute for Quantum Electronics, ETH Zürich

Nature, 2021, vol. 595, issue 7865, 53-57

Abstract: Abstract When the Coulomb repulsion between electrons dominates over their kinetic energy, electrons in two-dimensional systems are predicted to spontaneously break continuous-translation symmetry and form a quantum crystal1. Efforts to observe2–12 this elusive state of matter, termed a Wigner crystal, in two-dimensional extended systems have primarily focused on conductivity measurements on electrons confined to a single Landau level at high magnetic fields. Here we use optical spectroscopy to demonstrate that electrons in a monolayer semiconductor with density lower than 3 × 1011 per centimetre squared form a Wigner crystal. The combination of a high electron effective mass and reduced dielectric screening enables us to observe electronic charge order even in the absence of a moiré potential or an external magnetic field. The interactions between a resonantly injected exciton and electrons arranged in a periodic lattice modify the exciton bandstructure so that an umklapp resonance arises in the optical reflection spectrum, heralding the presence of charge order13. Our findings demonstrate that charge-tunable transition metal dichalcogenide monolayers14 enable the investigation of previously uncharted territory for many-body physics where interaction energy dominates over kinetic energy.

Date: 2021
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DOI: 10.1038/s41586-021-03590-4

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