Collective photon emission and ferroelectric exciton ordering near Mott insulating state in WSe₂/WS₂ heterobilayers

Nature Materials (2026)Cite this article Spontaneous symmetry breaking, driven by competing interactions and quantum fluctuations, is fundamental to understanding ordered electronic phases. Although electrically neutral, optical excitations like excitons can interact through their dipole moment, raising the possibility of optically active ordered phases. The effects of spontaneous ordering on optical properties remains underexplored. The excitonic Mott insulating state recently observed in semiconducting moiré crystals may help clarify this question. Here we present evidence for an in-plane ferroelectric phase of dipolar moiré excitons driven by strong exciton–exciton interactions. We reveal a speed-up of photon emission at late times and low densities in excitonic decay. This counterintuitive behaviour is attributed to collective radiance, linked to the transition between disordered and symmetry-broken ferroelectric phases of moiré excitons. Our findings provide evidence for strong dipolar intersite interactions in moiré lattices, demonstrate collective photon emission as a probe for moiré quantum materials and a path for exploring cooperative optical phenomena in strongly correlated systems.This is a preview of subscription content, access via your institution Access Nature and 54 other Nature Portfolio journals Get Nature+, our best-value online-access subscription $32.99 / 30 days cancel any timeSubscribe to this journal Receive 12 print issues and online access $259.00 per yearonly $21.58 per issueBuy this articleUSD 39.95Prices may be subject to local taxes which are calculated during checkoutAll the data that support the findings of this study are reported in the Article and its Supplementary Information. Source data are provided with this paper.Cai, J. et al. Signatures of fractional quantum anomalous Hall states in twisted MoTe2. Nature 622, 63–68 (2023).Article CAS PubMed Google Scholar Park, H. et al. 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T.P. and J.K. acknowledge support from the European Union’s Horizon Europe research and innovation programme under the Marie Skłodowska-Curie grant agreement number 101106552 (QuLowD), from the Austrian Science Fund (grant number 10.55776/COE1) and the European Union (NextGenerationEU), and from the European Research Council through the ERC Synergy Grant SuperWave (grant number 101071882). Synthesis of WSe2 (S.L. and J.H.) was supported by the NSF MRSEC program through the Columbia University Center for Precision-Assembled Quantum Materials (DMR-2011738). K.W. and T.T. acknowledge support from the JSPS KAKENHI (grant numbers 21H05233 and 23H02052), the CREST (JPMJCR24A5), JST and World Premier International Research Center Initiative (WPI), MEXT, Japan.These authors contributed equally: Luka Matej Devenica, Zach Hadjri, Jan Kumlin.Department of Quantum Matter Physics, University of Geneva, Geneva, Geneva, SwitzerlandLuka Matej Devenica, Zach Hadjri, Runtong Li, Weijie Li & Ajit SrivastavaDepartment of Physics, Emory University, Atlanta, USALuka Matej Devenica, Daniel Suárez-Forero, Klevis Domi, Bosai Lyu, Ludivine Fausten, Valeria Vento, Nicolas Ubrig & Ajit SrivastavaInstitute for Theoretical Physics, TU Wien, Vienna, AustriaJan Kumlin & Thomas PohlDepartment of Mechanical Engineering, Columbia University, New York, NY, USASong Liu & James HoneInstitute of Microelectronics, Chinese Academy of Sciences, Beijing, ChinaSong LiuResearch Center for Electronic and Optical Materials, National Institute for Materials Science, Tsukuba, JapanKenji WatanabeInternational Center for Materials Nanoarchitectonics, National Institute for Materials Science, Tsukuba, JapanTakashi TaniguchiSearch author on:PubMed Google ScholarSearch author on:PubMed Google ScholarSearch author on:PubMed Google ScholarSearch author on:PubMed Google ScholarSearch author on:PubMed Google ScholarSearch author on:PubMed Google ScholarSearch author on:PubMed Google ScholarSearch author on:PubMed Google ScholarSearch author on:PubMed Google ScholarSearch author on:PubMed Google ScholarSearch author on:PubMed Google ScholarSearch author on:PubMed Google ScholarSearch author on:PubMed Google ScholarSearch author on:PubMed Google ScholarSearch author on:PubMed Google ScholarSearch author on:PubMed Google ScholarSearch author on:PubMed Google ScholarA.S., T.P., L.M.D., Z.H. and D.S.-F. conceived the project. K.W. and T.T. provided the hBN crystals, and S.L. and J.H. provided the WSe2 crystals. L.M.D., B.L., W.L., Z.H. and L.F. prepared the samples. L.M.D., Z.H., R.L., D.S.-F., K.D., B.L., V.V., N.U. and L.F. carried out the measurements. J.K. and T.P. developed the theoretical model and conducted the Monte Carlo simulations. A.S. and T.P. supervised the project. All authors were involved in the analysis of the experimental data and contributed extensively.Correspondence to Daniel Suárez-Forero, Thomas Pohl or Ajit Srivastava.The authors declare no competing interests.Nature Materials thanks the anonymous reviewers for their contribution to the peer review of this work.Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.Supplementary Figs. 1–17 and Notes 1–5.Statistical source data.Statistical source data.Statistical source data.Statistical source data.Springer Nature or its licensor (e.g. a society or other partner) holds exclusive rights to this article under a publishing agreement with the author(s) or other rightsholder(s); author self-archiving of the accepted manuscript version of this article is solely governed by the terms of such publishing agreement and applicable law.Reprints and permissionsDevenica, L.M., Hadjri, Z., Kumlin, J. et al. Collective photon emission and ferroelectric exciton ordering near Mott insulating state in WSe2/WS2 heterobilayers. Nat. Mater. (2026). https://doi.org/10.1038/s41563-025-02476-4Download citationReceived: 05 March 2025Accepted: 19 December 2025Published: 29 January 2026Version of record: 29 January 2026DOI: https://doi.org/10.1038/s41563-025-02476-4Anyone you share the following link with will be able to read this content:Sorry, a shareable link is not currently available for this article. Provided by the Springer Nature SharedIt content-sharing initiative