Resonant chiral dressing by amplitude fluctuations in a ferroaxial electronic crystal

Nature Physics (2026)Cite this article Symmetry provides a unifying framework for understanding the ordering and dynamics of matter, and imposes constraints on the interactions between distinct collective excitations. In crystalline solids, these constraints are expressed through selection rules that prohibit harmonic coupling between zone-centre modes that transform under inequivalent irreducible representations. Although anharmonic processes can mediate coupling across distinct symmetry sectors, direct evidence for such mechanisms under thermodynamic equilibrium has not yet been shown. Here we demonstrate a dynamical interaction between modes of different symmetry in a ferroaxial charge density wave, a complex ordered state in which electronic modulations intertwine with rotational lattice distortions to break multiple mirror symmetries. Our helicity-resolved Raman micro-spectroscopy can access individual ferroaxial domains and reveals a temperature-dependent interplay between phonons and charge order amplitude fluctuations with a distinct symmetry character. We refer to this phenomenon as resonant chiral dressing. We propose a microscopic model that attributes this phenomenon to the dynamical dressing of phonons with collective charge order fluctuations, a process that involves the planar chirality of the underlying electronic state. These results establish order parameter dynamics as a route to mediate otherwise symmetry-forbidden interactions.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 checkoutSource data are provided with this paper.Landau, L. D. et al. On the theory of phase transitions. Zh. Eksp. Teor. Fiz 7, 19–32 (1937).

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Phys. 60, 1129–1181 (1988).Article ADS Google Scholar Download referencesWe acknowledge X. Li and R. Merlin for insightful discussions and M. Rerrer and M. v. Heek for their support during the resonance Raman measurements. E.B.’s group at the University of Texas at Austin gratefully acknowledges financial support from Love, Tito’s for the sample preparation activities. Work in E.B.’s group was primarily supported by the W. M. Keck Foundation under grant 996588 (to F.B. for data taking, analysis and manuscript writing), the National Science Foundation under grant DMR-2308817 (to X.P. for data taking, analysis and manuscript writing), the Robert A. Welch Foundation under grant F-2092-20250403 (to F.Y.G. for setup construction), ARL-UT Austin Cooperative Agreement W911NF-21-2-0185 (to W.Y. for data taking), the Applied Research Laboratories at UT Austin (to S.F. for data taking), the Air Force Office of Scientific Research under Young Investigator Program award FA9550-24-1-0097 (to S.Z. for experimental support) and the Alfred P. Sloan Foundation (to E.B. for data interpretation, manuscript writing and project supervision). F.B. acknowledges additional support from the Swiss NSF under fellowship P500PT_214437. Part of the experiments were performed at the user facility supported by the National Science Foundation through the Center for Dynamics and Control of Material under Cooperative Agreement DMR-2308817 and Major Research Instrumentation (MRI) program DMR-2019130. D.S. was supported by the Gwangju Institute of Science and Technology (GIST) research fund (Future-leading Specialized Research Project, 2025). The computational work was supported by the National Supercomputing Center with supercomputing resources including technical support (KSC-2025-CRE-0001). E.V.B. acknowledges funding from the European Union’s Horizon Europe research and innovation program under Marie Skłodowska-Curie grant agreement number 101106809. This work was supported in part by the European Research Council (ERC-2024-SyG-101167294; UnMySt), the Cluster of Excellence: Advanced Imaging of Matter (AIM) and Grupos Consolidados UPV/EHU (IT1249-19). L.B. acknowledges financial support from the European Union under project MORE-TEM ERC-SYN (number 951215), Sapienza University under project Ateneo (RM123188E357C540 and RP124190A63FAA97) and Italian MIUR under project PRIN2022-CoInEx (2022WS9MS4). The work at the University of Hamburg was supported by the German Research Foundation (DFG) under grant number RU 773/8-3. A.R. acknowledges support from the Max Planck-New York City Center for Non-Equilibrium Quantum Phenomena.

The Flatiron Institute is a division of the Simons Foundation.These authors contributed equally: Francesco Barantani, Xinyue Peng.Department of Physics and Center for Complex Quantum Systems, The University of Texas at Austin, Austin, TX, USAFrancesco Barantani, Xinyue Peng, Frank Y. Gao, Wenjing You, Sebastian Fava, Shangjie Zhang & Edoardo BaldiniMax Planck Institute for the Structure and Dynamics of Matter, Hamburg, GermanyEmil Viñas Boström & Angel RubioNano-Bio Spectroscopy Group, Departamento de Física de Materiales, Universidad del País Vasco, San Sebastián, SpainEmil Viñas Boström & Angel RubioInstitute of Nanostructure and Solid State Physics, University of Hamburg, Hamburg, GermanyPatrick Klein, Tomke Glier & Michael RübhausenDepartment of Physics and Photon Science, Gwangju Institute of Science and Technology (GIST), Gwangju, Republic of KoreaDaeheon Kim & Dongbin ShinInstitute of Experimental and Applied Physics, Kiel University, Kiel, GermanyFlorian K. Diekmann & Kai RossnagelDepartment of Mechanical Engineering, The University of Texas at Austin, Austin, TX, USAJianshi ZhouInstitute of Physics, École Polytechnique Fédérale de Lausanne (EPFL), Lausanne, SwitzerlandHelmuth BergerRuprecht Haensel Laboratory, Deutsches Elektronen-Synchrotron DESY, Hamburg, GermanyKai RossnagelDepartment of Physics and ISC-CNR, Sapienza University of Rome, Rome, ItalyLara BenfattoInitiative for Computational Catalysis, The Flatiron Institute, New York, NY, USAAngel RubioSearch 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 ScholarSearch author on:PubMed Google ScholarSearch author on:PubMed Google ScholarE.B. conceived the study. F.B., X.P., W.Y. and E.B. designed the research. F.B., X.P., F.Y.G., W.Y. and S.Z. performed the temperature-dependent Raman experiments under the supervision of E.B. P.K., T.G., S.F. and M.R. performed the photon-energy-dependent Raman measurements at room temperature. H.B., F.K.D. and K.R. grew the single crystals, and J.Z. characterized them using electrical transport. X.P. exfoliated the flakes from the single crystals. F.B. and X.P. carried out the temperature-dependent electron diffraction measurements. F.B. and X.P. analysed all experimental data. E.V.B. developed the microscopic theories under the supervision of L.B. and A.R. D.K. and D.S. performed first-principles calculations of lattice dynamics. F.B., X.P., E.V.B., L.B. and E.B. prepared the manuscript with input from all authors. E.B. supervised the overall project.Correspondence to Edoardo Baldini.The authors declare no competing interests.Nature Physics thanks Ge He and the other, anonymous, reviewer(s) 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.a, Deconvoluted Raman intensity spectra measured for different incident photon energies in the co-rotating polarization (σ+σ+ and σ−σ−). b, Corresponding spectra in the contra-rotating channels (σ+σ− and σ−σ+). c, ROA extracted from the spectra in (b). d, ROA averaged over 60-80 cm−1 (top) and 80-100 cm−1 (bottom) as a function of incident photon energy. Two distinct resonances at 2.0 and 2.4 eV emerge, fully consistent with the assumptions underlying our microscopic model.Source dataPhonons I-V (defined in Fig. 3) are shown in panels a–e. The plotted intensity corresponds to the integrated area of the Voigt fits for each mode. Notably, phonon II (panel b) exhibits an increase in intensity above 150 K. The central value corresponds to the fitted amplitude parameter. Error bars are estimated as the square root of the extracted intensity, assuming Poisson shot noise of the underlying photon counts.Source dataTemperature dependence of the static (solid blue), dynamical (red), and total (dashed blue) ROA for phonons I–V (panels a–e), as defined in Fig. 3. These curves result from fitting the data in Fig. 4 using our microscopic model. The static and total ROA correspond to the blue vertical axis (left), while the dynamical component corresponds to the red vertical axis (right). Note that, although \({R}_{0}(T)={\bar{R}}_{0}{\Delta }_{0}(T)\) (see Supplementary Note S15), the overall temperature dependence associated with Δ0(T) cancels out in the ROA defined in Eq. (1).Source dataSupplementary Notes 1–18, Tables 1–10 and Figs. 1–35.Atomic trajectories in AL-stacked 1T-TaS2 obtained from molecular dynamics simulation following radial compression of the Star-of-David CDW pattern.Atomic trajectories in 4Hb-TaS2 obtained from molecular dynamics simulation following radial compression of the Star-of-David CDW pattern.Unprocessed temperature-dependent helicity-resolved Raman intensity spectra of 4Hb-TaS2.Unprocessed temperature-dependent helicity-resolved Raman intensity spectra of 1T-TaS2.Data from Fig. 1c,e.Data for Fig. 2a–f. Each Excel sheet contains data from each panel as labelled.Data for Fig. 3a–f. Each Excel sheet contains data from each panel as labelled.Data for Fig. 4a–f. Each Excel sheet contains data from each panel as labelled.Data for Extended Data Fig. 1a–f. Each Excel sheet contains data from each panel as labelled.Data for Extended Data Fig. 2a–e. Each Excel sheet contains data from each panel as labelled.Data for Extended Data Fig. 3a–d. Each Excel sheet contains data from each panel as labelled.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 permissionsBarantani, F., Peng, X., Viñas Boström, E. et al. Resonant chiral dressing by amplitude fluctuations in a ferroaxial electronic crystal. Nat. Phys. (2026). https://doi.org/10.1038/s41567-026-03241-3Download citationReceived: 31 July 2025Accepted: 04 March 2026Published: 01 May 2026Version of record: 01 May 2026DOI: https://doi.org/10.1038/s41567-026-03241-3Anyone 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