Observation of a hidden charge density wave liquid

Nature Physics (2025)Cite this article Charge density waves, electronic crystals that form within a host solid, have long been theorized to melt into a spatially textured electronic liquid. Although such liquid charge density waves have not been previously observed, they may be central to the phase diagrams of correlated electron systems, including high-temperature superconductors and quantum Hall states. In 1T-TaS2, a promising material for hosting a liquid charge density wave, a structural phase transition hinders observation. Here we use femtosecond light pulses to bypass this transition, revealing how topological defect dynamics govern hidden charge density wave correlations. Following photoexcitation, charge density wave diffraction peaks broaden azimuthally, indicating the emergence of a hexatic state. At elevated temperatures, photoexcitation fully destroys both translational and orientational orders, leaving only a ring of diffuse scattering—the hallmark of a liquid charge density wave. These findings offer compelling evidence for a defect-unbinding transition to a charge density wave liquid. More broadly, this approach demonstrates a route to uncover electronic phases obscured by intervening transitions in thermal equilibrium.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 checkoutThe data that support the findings of this study are provided in the Article. Source data are provided with this paper. These data are also available via Zenodo at https://doi.org/10.5281/zenodo.15453892 (ref. 56). Additional data related to the paper are available from the corresponding author upon request.The code used to produce the figures in this work is available via Zenodo at https://doi.org/10.5281/zenodo.17383782 (ref. 57).Anderson, M. H. et al. Observation of Bose-Einstein condensation in a dilute atomic vapor. Science 269, 198–201 (1995).Article Google Scholar Davis, K. B. et al. Bose-Einstein condensation in a gas of sodium atoms. Phys. Rev. Lett. 75, 3969–3973 (1995).Article Google Scholar Tenney, C. M., Croft, Z. F. & McMahon, J. M. Metallic hydrogen: a liquid superconductor? J. Phys. Chem. C 125, 23349–23355 (2021).Article Google Scholar Leggett, A. J. in PWA90: A Lifetime of Emergence (eds Chandra, P., Coleman, P., Kotliar, G., Ong, P., Stein, D. L. & Yu, C.) 97–103 (World Scientific, 2016).Stojchevska, L. et al. Ultrafast switching to a stable hidden quantum state in an electronic crystal. Science 344, 177–180 (2014).Article ADS Google Scholar Kogar, A. et al. Light-induced charge density wave in LaTe3. Nat. Phys. 16, 159–163 (2020).Article Google Scholar Fausti, D. et al. Light-induced superconductivity in a stripe-ordered cuprate. Science 331, 189–191 (2011).Article ADS Google Scholar Disa, A. S. et al. Photo-induced high-temperature ferromagnetism in YTiO3. Nature 617, 73–78 (2023).Article ADS Google Scholar Mitrano, M. et al. Possible light-induced superconductivity in K3C60 at high temperature. Nature 530, 461–464 (2016).Article ADS Google Scholar Nova, T. F. et al. Metastable ferroelectricity in optically strained SrTiO3. Science 364, 1075–1079 (2019).Article ADS Google Scholar Li, X. et al. Terahertz field–induced ferroelectricity in quantum paraelectric SrTiO3. Science 364, 1079–1082 (2019).Article ADS Google Scholar Dai, H. & Lieber, C. M. Solid-hexatic-liquid phases in two-dimensional charge-density waves. Phys. Rev. Lett. 69, 1576–1579 (1992).Article ADS Google Scholar Dai, H., Chen, H. & Lieber, C. M. Weak pinning and hexatic order in a doped two-dimensional charge-density-wave system. Phys. Rev. Lett. 66, 3183 (1991).Article ADS Google Scholar Hayden, S. M. & Tranquada, J. M. Charge correlations in cuprate superconductors. Annu. Rev. Condens. Matter Phys. 15, 215 (2024).Article ADS Google Scholar Subires, D. et al. Frustrated charge density wave and quasi-long-range bond-orientational order in the magnetic kagome FeGe. Nat. Commun. 16, 4091 (2025).Article ADS Google Scholar Kivelson, S. A., Fradkin, E. & Emery, V. J. Electronic liquid-crystal phases of a doped Mott insulator. Nature 393, 550–553 (1998).Article ADS Google Scholar Delacrétaz, L. V. et al. Theory of hydrodynamic transport in fluctuating electronic charge density wave states. Phys. Rev. B 96, 195128 (2017).Article ADS Google Scholar Taraphder, A. et al. Preformed excitonic liquid route to a charge density wave in 2H-TaSe2. Phys. Rev. Lett. 106, 236405 (2011).Article ADS Google Scholar Snow, C. S. et al. Quantum melting of the charge-density-wave state in 1T-TiSe2. Phys. Rev. Lett. 91, 136402 (2003).Article ADS Google Scholar Ciftja, O., Lapilli, C. M. & Wexler, C. Liquid crystalline states for two-dimensional electrons in strong magnetic fields. Phys. Rev. B 69, 125320 (2004).Article ADS Google Scholar Wexler, C. & Ciftja, O. Liquid crystalline states in quantum Hall systems. J. Phys.: Condens. Matter 14, 3705 (2002).ADS Google Scholar Fradkin, E. & Kivelson, S. A. Liquid-crystal phases of quantum Hall systems. Phys. Rev. B 59, 8065 (1999).Article ADS Google Scholar Nie, L., Tarjus, G. & Kivelson, S. A. Quenched disorder and vestigial nematicity in the pseudogap regime of the cuprates. Proc. Natl Acad. Sci. USA 111, 7980–7985 (2014).Article ADS Google Scholar Milward, G. C., Calderón, M. J. & Littlewood, P. B. Electronically soft phases in manganites. Nature 433, 607–610 (2005).Article ADS Google Scholar Nelson, D. R. & Halperin, B. I. Dislocation-mediated melting in two dimensions. Phys. Rev. B 19, 2457–2484 (1979).Article ADS Google Scholar Halperin, B. I. & Nelson, D. R. Theory of two-dimensional melting. Phys. Rev. Lett. 41, 121–124 (1978).Article ADS MathSciNet Google Scholar Kosterlitz, J. M. Kosterlitz–Thouless physics: a review of key issues. Rep. Prog. Phys. 79, 026001 (2016).Article ADS Google Scholar Keim, P., Maret, G. & von Grünberg, H. H. Frank’s constant in the hexatic phase. Phys. Rev. E 75, 031402 (2007).Article ADS Google Scholar Kusner, R. E. et al. Two-stage melting of a two-dimensional collodial lattice with dipole interactions. Phys. Rev. Lett. 73, 3113–3116 (1994).Article ADS Google Scholar Troyanovski, A. M. et al. STM imaging of flux line arrangements in the peak effect regime. Phys. Rev. Lett. 89, 147006 (2002).Article ADS Google Scholar Guillamón, I. et al. Direct observation of melting in a two-dimensional superconducting vortex lattice. Nat. Phys. 5, 651–655 (2009).Article Google Scholar Roy, I. et al. Melting of the vortex lattice through intermediate hexatic fluid in an a-MoGe thin film. Phys. Rev. Lett. 122, 047001 (2019).Article ADS Google Scholar Brock, J. D. et al. Orientational and positional order in a tilted hexatic liquid-crystal phase. Phys. Rev. Lett. 57, 98–101 (1986).Article ADS Google Scholar Cheng, M. et al. Observation of two-dimensional hexatic behavior in free-standing liquid-crystal thin films. Phys. Rev. Lett. 61, 550–553 (1988).Article ADS Google Scholar Sharma, R. et al. Thermal melting of a vortex lattice in a quasi two-dimensional Bose gas. Phys. Rev. Lett. 133, 143401 (2024).Article ADS Google Scholar Huang, P. et al. Melting of a skyrmion lattice to a skyrmion liquid via a hexatic phase. Nat. Nanotechnol. 15, 761–767 (2020).Article ADS Google Scholar Gallet, F. et al. Fluctuations and shear modulus of a classical two-dimensional electron solid: experiment. Phys. Rev. Lett. 49, 212–215 (1982).Article ADS Google Scholar Knighton, T. et al. Evidence of two-stage melting of Wigner solids. Phys. Rev. B 97, 085135 (2018).Article ADS Google Scholar Sung, S. H. et al. Endotaxial stabilization of 2D charge density waves with long-range order. Nat. Commun. 15, 1403 (2024).Article ADS Google Scholar Domröse, T. et al. Light-induced hexatic state in a layered quantum material. Nat. Mater. 22, 1345–1351 (2023).Article ADS Google Scholar Givens, F. L. & Fredericks, G. E. Thermal expansion op NbSe2 and TaS2. J. Phys. Chem. Solids 38, 1363–1365 (1977).Article ADS Google Scholar Gruner, G. Density Waves in Solids (CRC Press, 2018).Thomson, R. E. et al. Local charge-density-wave structure in 1T-TaS2 determined by scanning tunneling microscopy. Phys. Rev. B 38, 10734–10743 (1988).Article ADS Google Scholar Rossnagel, K. On the origin of charge-density waves in select layered transition-metal dichalcogenides. J. Phys.: Condens. Matter 23, 213001 (2011).ADS Google Scholar Sutter, T. M. et al. Vector-based feedback of continuous wave radiofrequency compression cavity for ultrafast electron diffraction. Struct. Dyn. 11, 024303 (2024).Article Google Scholar Zong, A. et al. Evidence for topological defects in a photoinduced phase transition. Nat. Phys. 15, 27–31 (2019).Article Google Scholar Cheng, Y. et al. Light-induced dimension crossover dictated by excitonic correlations. Nat. Commun. 13, 963 (2022).Article ADS Google Scholar Gonzalez-Vallejo, I. et al. Time-resolved structural dynamics of the out-of-equilibrium charge density wave phase transition in GdTe3. Struct. Dyn. 9, 014502 (2022).Article Google Scholar Trigo, M. et al. Coherent order parameter dynamics in SmTe3. Phys. Rev. B 99, 104111 (2019).Article ADS Google Scholar Han, T. R. T. et al. Structural dynamics of two-dimensional charge-density waves in CeTe3 investigated by ultrafast electron crystallography. Phys. Rev. B 86, 075145 (2012).Article ADS Google Scholar Zurek, W. H., Dorner, U. & Zoller, P. Dynamics of a quantum phase transition. Phys. Rev. Lett. 95, 105701 (2005).Article ADS Google Scholar Dziarmaga, J. Dynamics of a quantum phase transition: exact solution of the quantum Ising model. Phys. Rev. Lett. 95, 245701 (2005).Article ADS Google Scholar Polkovnikov, A. Universal adiabatic dynamics in the vicinity of a quantum critical point. Phys. Rev. B 72, 161201 (2005).Article ADS Google Scholar Di Salvo, F. J. et al. Effects of doping on charge-density waves in layer compounds. Phys. Rev. B 12, 2220 (1975).Article ADS Google Scholar Di Salvo, F. J. et al. Preparation and properties of a new polytype of tantalum disulfide (4Hb-TaS2). J. Phys. Chem. Solids 34, 1357–1362 (1973).Article ADS Google Scholar Lee, J. S. H. Observation of a hidden charge density wave liquid. Zenodo https://doi.org/10.5281/zenodo.15453892 (2025).Sutter, T., Lee, J., Karapetrov, G., Musumeci, P. & Kogar, A. Two dimensional molecular dynamics simulation (KTHNY). Zenodo https://doi.org/10.5281/zenodo.17383782 (2025).Download referencesWe thank S. E. Brown, R. Bruinsma and X. Zhang for insightful discussions regarding this work. We thank M. Rasiah, S. Wang, J. Higgins, A. Ody and A. Kulkarni for their instrumentation work in the kiloelectronvolt UED setup at University of California, Los Angeles. We acknowledge support from the US Department of Energy, Office of Science, Office of Basic Energy Sciences, under award number DE-SC0023017 (A.K.; data taking, data analysis and manuscript writing). We also acknowledge support from STROBE: a National Science Foundation Science and Technology Center under grant number DMR-1548924 (A.K. and P.M.; instrumentation).These authors contributed equally: Joshua S. H. Lee, Thomas M. Sutter.Department of Physics and Astronomy, University of California Los Angeles, Los Angeles, CA, USAJoshua S. H. Lee, Thomas M. Sutter, Pietro Musumeci & Anshul KogarDepartment of Physics, Drexel University, Philadelphia, PA, USAGoran KarapetrovSearch author on:PubMed Google ScholarSearch author on:PubMed Google ScholarSearch author on:PubMed Google ScholarSearch author on:PubMed Google ScholarSearch author on:PubMed Google ScholarJ.S.H.L. and T.M.S. performed the diffraction measurements. J.S.H.L. and T.M.S. prepared the samples for measurements. J.S.H.L. and T.M.S. built the kiloelectronvolt UED beamline at University of California, Los Angeles, under the supervision of A.K. and P.M. G.K. grew the crystals for the experiment. J.S.H.L. performed the data analysis with theoretical input from T.M.S. and A.K. T.M.S. performed the molecular dynamics simulations. J.S.H.L., T.M.S. and A.K. wrote the paper with important input from all other authors. The work was supervised by A.K.Correspondence to Anshul Kogar.The authors declare no competing interests.Nature Physics thanks Haiyun Liu, Chih-Wei Luo 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.Supplementary Notes I–XIV, Figs. 1–12 and references.Animated version of Fig. 2e,j, but for all times t rather than only at selected times. The dynamics at the initial temperatures of 360 K and 520 K are animated side by side for comparison.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 permissionsLee, J.S.H., Sutter, T.M., Karapetrov, G. et al. Observation of a hidden charge density wave liquid. Nat. Phys. (2025). https://doi.org/10.1038/s41567-025-03108-zDownload citationReceived: 05 June 2025Accepted: 22 October 2025Published: 30 December 2025Version of record: 30 December 2025DOI: https://doi.org/10.1038/s41567-025-03108-zAnyone 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