Driving Floquet physics with excitonic fields

Nature Physics (2026)Cite this article Floquet engineering, in which an intense optical field modifies the electronic structure of a material, offers a route to the control of quantum and topological properties. However, it is challenging to realize this in experiments due to relatively weak light–matter coupling and the dominance of detrimental effects, such as multi-photon absorption and sample heating. Here we use time- and angle-resolved photoemission spectroscopy to show that in a monolayer semiconductor, Floquet effects caused by an excitonic field—the time-periodic oscillations of the self-energy of an electron bound to a hole—are two orders of magnitude stronger and persist longer than optically driven counterparts. Our measurements directly capture the hybridization between the exciton-dressed conduction band and the valence band in two-dimensional semiconductors, in agreement with first-principles calculations. The onset of this hybridization with increasing exciton density also correlates with the Bose–Einstein condensation to Bardeen–Cooper–Schrieffer crossover, extensively discussed in theory for non-equilibrium excitonic insulators. These results establish exciton-driven Floquet engineering as a means for studying correlated electronic phases.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 supports the findings of this work are available upon request to the corresponding authors.Lloyd-Hughes, J. et al. The 2021 ultrafast spectroscopic probes of condensed matter roadmap. J. Phys.: Condens. Matter 33, 353001 (2021). Google Scholar de la Torre, A. et al. Colloquium: nonthermal pathways to ultrafast control in quantum materials. Rev. Mod. Phys. 93, 041002 (2021).Article ADS Google Scholar Giustino, F. et al. The 2021 quantum materials roadmap. J. Phys.: Mater. 3, 042006 (2020).

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J.M. acknowledges support from the JSPS KAKENHI (Grant Number 24K00561). K.M.D. acknowledges support from the JST FOREST (Grant number 23718777) and the JSPS KAKENHI (Grant numbers 22K18270, 24H00191 and 23K25807). F.H.d.J. acknowledges support from the Center for Non-Perturbative Studies of Functional Materials Under Non-Equilibrium Conditions, funded by the US Department of Energy (DOE), Office of Science (Contract DE-AC52-07NA27344). This work uses codes developed by the Center for Computational Study of Excited State Phenomena in Energy Materials, which is funded by the DOE Office of Science (Contract No. DE-AC02-05CH11231). We acknowledge support for computational resources and storage provided by the National Energy Research Scientific Computing Center, a DOE Office of Science User Facility (Contract No. DE-AC02-05CH11231) and the National Center for High-performance Computing. D.Y.Q. acknowledges support from the US DoE, Office of Science, Basic Energy Sciences (Early Career Award No. DE-SC0021965). F.B. and K.E.J.G. acknowledge funding support from the Agency for Science, Technology and Research (Grant No. 21709) and the Singapore National Research Foundation (Grant No. CRP21-2018-0001). 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. G.S. and E.P. acknowledge funding support from Ministero Università e Ricerca PRIN (Grant Agreement No. 2022WZ8LME), INFN (Project TIME2QUEST) and the European Research Council MSCA-ITN TIMES (Grant Agreement No. 101118915). M.G.M. acknowledges the support from the Brazilian funding agencies Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), Fundação de Amparo à Pesquisa do Estado do Rio de Janeiro (FAPERJ), Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) and Institutos Nacionais de Ciência e Tecnologia (INCTs) em Nanomateriais de Carbono e Materiais 2D e Materials Informatics.These authors contributed equally: Vivek Pareek, David R. Bacon, Xing Zhu.Femtosecond Spectroscopy Unit, Okinawa Institute of Science and Technology Graduate University, Onna, JapanVivek Pareek, David R. Bacon, Xing Zhu, Nicholas S. Chan, Joel Pérez Urquizo, Michael K. L. Man, Julien Madéo & Keshav M. DaniDepartment of Physics, California Institute of Technology, Pasadena, CA, USAVivek PareekInstitute of Atomic and Molecular Sciences, Academia Sinica, and Physics Division, National Center of Theoretical Sciences, Taipei, TaiwanYang-Hao ChanInstitute of Materials Research and Engineering (IMRE), Agency for Science, Technology and Research (A*STAR), Singapore, SingaporeFabio Bussolotti & Kuan Eng Johnson GohInstituto de Física, Universidade Federal do Rio de Janeiro, Rio de Janeiro, BrazilMarcos G. MenezesResearch Center for Functional Materials, National Institute for Materials Science, Tsukuba, JapanKenji WatanabeInternational Center for Materials Nanoarchitectonics, National Institute for Materials Science, Tsukuba, JapanTakashi TaniguchiPhysics Department, University of Rome Tor Vergata, Rome, ItalyEnrico Perfetto & Gianluca StefanucciINFN, Sezione di Roma Tor Vergata, Rome, ItalyEnrico Perfetto & Gianluca StefanucciDepartment of Materials Science, Yale University, New Haven, CT, USADiana Y. QiuDepartment of Physics, National University of Singapore, Singapore, SingaporeKuan Eng Johnson GohDivision of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore, SingaporeKuan Eng Johnson GohDepartment of Materials Science and Engineering, Stanford University, Stanford, CA, USAFelipe H. da JornadaStanford PULSE Institute, SLAC National Accelerator Laboratory, Menlo Park, CA, USAFelipe H. da JornadaSearch 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 ScholarV.P., D.R.B. and X.Z. performed the TR-ARPES measurements, the sample characterization and analysis of the data, with assistance from J.P.U., M.K.L.M. and J.M. and under the supervision of K.M.D. Y.-H.C. implemented the theoretical simulations, with assistance from D.Y.Q. and under the supervision of F.H.d.J. M.G.M. contributed to the exciton-Floquet physics, under the supervision of F.H.d.J. E.P. and G.S. contributed to the understanding of the physics of excitons at high densities. K.E.J.G. developed the chemical vapour deposition growth process for large 1L WS2 samples. F.B. prepared the samples with assistance from N.S.C. and V.P. and under the supervision of K.E.J.G. and K.M.D. K.W. and T.T. provided the bulk hBN crystals for the study. F.H.d.J. and K.M.D. conceived and designed the study. All authors contributed to the writing and reviewing of the paper.Correspondence to Felipe H. da Jornada or Keshav M. Dani.J.M., M.K.L.M. and K.M.D. are inventors on a granted patent related to this work BS filed by the OIST School Corporation (US patent 11,372,199). K.E.J.G. is an inventor on a patent application related to this work filed by the Agency for Science, Technology and Research (Singapore) (Patent SG2022050106 published on 9 September 2022). The other authors declare no competing interests.Nature Physics 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.We measured the absorption and the photoemission excitation (PEE) spectra at 100 K from the 1 L WS2 sample. The PEE spectrum was obtained by integrating the photoemission signal from the electron part of the excitons at zero pump-probe time delay. The black arrow indicates the energy of the pump pulse used to access optically driven Floquet physics. The red arrow indicates the pump energy used for the exciton driven Floquet process. We measure the linewidth of our sample to be 8 meV by fitting a gaussian function (solid blue line) to the absorption spectra at 100 K.a) A 3D dataset showing the 6 K points of the 1 L WS2 sample obtained from ToF MM. The red hexagon marks the first BZ with the red dashed line showing the cut along the Γ-K-M used to obtain the band structures in Fig. 1d,e. b) The E-K cuts like the cuts shown in Fig. 1d,e. The dotted line shows EDCs obtained around the K point for (c). The inset shows the schematic diagram for the cuts. c) The valence band EDC at the K point with the calculated Shirley background, d) Valence band EDC after subtraction is fitted to a double gaussian function to get the peak position for both VB1 and VB2 to calculate the exciton-driven hybridization effect.a-d) Dispersion of the valence band replica with decreasing exciton densities obtained by single gaussian fitting. e) Dispersion of VB1 and VB2 for no pump case for comparison (f-i) Dispersion of VB1 and VB2 with decreasing exciton densities obtained by fitting a double gaussian function to the Shirley-corrected EDCs.Energy distribution curves (EDCs) for the exciton replica at selected k positions around the K point (0,0) for a) low exciton density and b) high exciton density. The red solid lines are single gaussian fitting to the EDCs. The center position of the gaussian fitting is marked by the grey triangles. c) Comparison between the dispersion of the exciton replica at low (grey circles) and high (orange circles) with the ground state valence band (dashed line). The valence band dispersion was shifted up in energy by 2.1 eV for comparison. For the low exciton density, we clearly observe a parabolic negative dispersion mimicking the valence band. For the high exciton density case, the replica dispersion shows the distinct Mexican-hat-like dispersion.a) Difference in the dispersion for VB1 for different exciton densities with respect to the no pump VB1 dispersion showing drastic changes near the K point, b) Difference in the dispersion for VB2 with respect to the no pump VB2 dispersion showing no substantial change in general.a) Unperturbed bandstructure at the K valley. b) Bandstructure after above bandgap (ℏν = 3 eV) excitation. We observe the characteristic positive dispersion from the free carriers occupying the conduction band but do not observe the Mexican-hat-like dispersion in the bandstructure for this case. c) Bandstructure after A exciton resonant (ℏν = 2.1 eV) excitation. We observe the hallmark Mexican-hat-like dispersion due to the excitonic field. Both the experiments were performed at 100 K with ~2×1012cm −2 excited photocarriers in b) and ~2×1012cm −2 excitons in c). d) The strength of the hybridization (ΔEX) extracted for different pump wavelengths around the exciton resonance (yellow circles) matches the A exciton absorption peak (blue) confirming the correlation between the excitons and the Mexican-hat-like dispersion. The pump power was kept constant (10 mW) for all the wavelengths. The black curve is a guide to the eye.a) Energy integrated momentum image of the top of the K valley (VB1) with an exciton density nX = 3 × 1012 cm−2. The red boxes indicate the region used to normalize the intensity for the un-photoexcited and photoexcited case. b) Energy integrated momentum image of the top of the K valley for the un-photoexcited case. c) The momentum distribution of the hole wavefunction obtained after taking the ratio of photoexcited and un-photoexcited bands in (a) and (b) respectively.Supplementary Figs. 1–6 and Discussion.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 permissionsPareek, V., Bacon, D.R., Zhu, X. et al. Driving Floquet physics with excitonic fields. Nat. Phys. (2026). https://doi.org/10.1038/s41567-025-03132-zDownload citationReceived: 23 May 2025Accepted: 11 November 2025Published: 19 January 2026Version of record: 19 January 2026DOI: https://doi.org/10.1038/s41567-025-03132-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