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Observation of excitonic Floquet states in a one-dimensional organic Mott insulator using mid-infrared pump near-infrared probe reflection spectroscopy

R. Ikeda1,*, D. Sakai1, T. Yamakawa1, T. Miyamoto1,2, H. Kishida3, T. Hasegawa4, and H. Okamoto1,†

  • *Contact author: r.ikeda@edu.k.u-tokyo.ac.jp
  • †Contact author: okamotoh@k.u-tokyo.ac.jp
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Phys. Rev. Research 7, 033230 – Published 9 September, 2025

DOI: https://doi.org/10.1103/rl4c-w66n

Abstract

When an electric field of light with a frequency of Ω is applied to a solid, Floquet states, consisting of sidebands with an interval of ℏΩ around an electronic state, are expected to be formed. However, only a few studies have experimentally detected such sidebands. Here, we apply mid-infrared pump near-infrared reflection probe spectroscopy to a one-dimensional Mott insulator, bis(ethylenedithio)tetrathiafulvalene-difluorotetracyanoquinodimethane (ET−F2TCNQ), to detect the transient change in reflectivity R, ΔR/R, due to the formation of excitonic Floquet states. Analyses, considering both odd- and even-parity excitons, demonstrate that the ΔR/R spectrum reflects the formation of the first-order Floquet sidebands of excitons, and its spectral shape strongly depends on the widths of excitonic states. The experimental and analytical approach reported here is effective in demonstrating excitonic Floquet states in various solids.

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Phys. Rev. Research 7, 033230– Published 9 September, 2025
  • Received 26 July 2024
  • Revised 3 May 2025
  • Accepted 31 July 2025
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

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