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Real-space imaging of thermally and photoinduced phase transition in quasi-one-dimensional organic complexes

Keiki Fukumoto* and Elizaveta Pyatenko†

Ken Onda and Takanori Tanaka

Koichi Kusakabe

Hideki Yamochi

Shin-ichi Adachi

Shin-ya Koshihara

  • Department of Chemistry, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan

  • Department of Material Science, Graduate School of Science, University of Hyogo, 3-2-1, Kouto, Kamigori-cho, Ako-gun, Hyogo 678-1297, Japan

  • Division of Chemistry, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan

  • *Contact author: keiki@post.kek.jp
  • †Present address: The Institute for Solid State Physics, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8581, Japan.
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Phys. Rev. Research 8, 033329 – Published 17 September, 2026

DOI: https://doi.org/10.1103/22k3-7nym

Abstract

Photoinduced phase transition (PIPT) involves substantial changes in both electronic and crystallographic structures caused by electron excitations. Because PIPT is ultrafast and exhibits inhomogeneous behavior, its fundamental processes, in particular, how the ultrafast dynamics of photoexcited electrons trigger lattice deformation and the timescales involved, remain poorly understood. In this study, phase transition and its spatial separation in organic charge-transfer complexes was investigated using photoemission electron microscopy with femtosecond pulsed laser excitation. First, the thermally induced phase transition was confirmed by imaging the morphology change and also by observing the change of spectral shape around the Fermi level. Second, the escape time of photoexcited electrons or the heat generated by the laser pulses is estimated by observing the morphology change depending on the laser repetition rate. Finally, the dynamics of the photoexcited electrons and the subsequent morphology change are directly visualized. The results show that an anisotropic morphology change is initiated following the accumulation of electrons in unoccupied states over approximately a picosecond.

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Phys. Rev. Research 8, 033329– Published 17 September, 2026
  • Received 29 April 2026
  • Accepted 22 July 2026
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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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