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<p>The complex phase diagram of 1T-TiSe<sub>2</sub> consists of a charge density wave (CDW) below 200 K, and CDW fluctuations of still unknown origin at higher temperatures. Here, we use time-resolved extreme ultraviolet momentum microscopy and density functional perturbation theory to uncover the formation mechanism of CDW fluctuations and their spectral features at 295 K. We investigated the transient dynamics of fluctuations upon nonresonant ultrafast photoexcitation, and directly correlate it with the CDW soft-phonon hardening. Surprisingly, our results show that the coherent amplitude mode modulating ultrafast CDW recovery persists above <i>T</i><sub>CDW</sub>, and reveal that CDW fluctuations are dominated by the electron-phonon interaction rather than excitonic correlations as commonly believed. Our findings on these microscopic CDW fluctuations clarify the complex interplay between electronic and lattice degrees of freedom at elevated temperatures and, therefore, could be useful in understanding the nature of the CDW phase transition in 1T-TiSe<sub>2</sub> and similar quantum materials.</p>

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Electron-phonon-dominated charge-density-wave fluctuations in TiSe2 accessed by ultrafast nonequilibrium dynamics

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年2月4日

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  • Sotirios Fragkos,
  • Hibiki Orio,
  • Nina Girotto Erhardt,
  • Akib Jabed,
  • Sarath Sasi,
  • Quentin Courtade,
  • Muthu P. T. Masilamani,
  • Maximilian Ünzelmann,
  • Florian Diekmann,
  • Baptiste Hildebrand,
  • Dominique Descamps,
  • Stéphane Petit,
  • Fabio Boschini,
  • Ján Minár,
  • Yann Mairesse,
  • Friedrich Reinert,
  • Kai Rossnagel,
  • Dino Novko,
  • Samuel Beaulieu,
  • Jakub Schusser

摘要

The complex phase diagram of 1T-TiSe2 consists of a charge density wave (CDW) below 200 K, and CDW fluctuations of still unknown origin at higher temperatures. Here, we use time-resolved extreme ultraviolet momentum microscopy and density functional perturbation theory to uncover the formation mechanism of CDW fluctuations and their spectral features at 295 K. We investigated the transient dynamics of fluctuations upon nonresonant ultrafast photoexcitation, and directly correlate it with the CDW soft-phonon hardening. Surprisingly, our results show that the coherent amplitude mode modulating ultrafast CDW recovery persists above TCDW, and reveal that CDW fluctuations are dominated by the electron-phonon interaction rather than excitonic correlations as commonly believed. Our findings on these microscopic CDW fluctuations clarify the complex interplay between electronic and lattice degrees of freedom at elevated temperatures and, therefore, could be useful in understanding the nature of the CDW phase transition in 1T-TiSe2 and similar quantum materials.