Journal Article

PUBDB-2026-01119

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Electron-phonon-dominated charge-density-wave fluctuations in TiSe$_2$ accessed by ultrafast nonequilibrium dynamics

Fragkos, S. ; Orio, H. (Corresponding author)Extern* ; Girotto Erhardt, N. ; Jabed, A. ; Sasi, S. ; Courtade, Q. ; Masilamani, M. P. T. ; Ünzelmann, M. ; Diekmann, F. ; Hildebrand, B. ; Descamps, D. ; Petit, S. ; Boschini, F. ; Minár, J. ; Mairesse, Y. ; Reinert, F. ; Rossnagel, K.DESY* ; Novko, D. ; Beaulieu, S. ; Schusser, J. (Corresponding author)Extern*

2026
Springer Nature London

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Please use a persistent id in citations: doi:10.1038/s42005-026-02521-x  doi:10.3204/PUBDB-2026-01119

Abstract: The complex phase diagram of 1T-TiSe$_2$ 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-TiSe$_2$ and similar quantum materials.

Note: AcknowledgementsWe thank Claude Monney for useful discussions. We thank Nikita Fedorov,Romain Delos, Pierre Hericourt, Rodrigue Bouillaud, Laurent Merzeau, andFrank Blais for technical assistance and Aymen Mahmoudi, Joel Morf, andFrederic Chassot for their assistance during STM measurements. J.S., S.S.,and J.M. would like to thank the QM4ST project with Reg. No.CZ.02.01.01/00/22_008/0004572, cofunded by the ERDF as part ofthe MŠMT. The research leading to these results has received funding fromLASERLAB-EUROPE (grant agreement no. 871124, European Union’sHorizon 2020 research and innovation programme). We acknowledge thenancial support of the IdEx University of Bordeaux / Grand ResearchProgram“GPR LIGHT”. We acknowledge support from ERC Starting GrantERC-2022-STG No.101076639, Quantum Matter Bordeaux, AAP CNRSTremplin, and AAP SMR from Université de Bordeaux. This work is part of theULTRAFAST and TORNADO projects of PEPR LUMA and was supported bythe French National Research Agency, as a part of the France 2030 program,under grants ANR-23-EXLU-0002 and ANR-23-EXLU-0004. SF acknowl-edges funding from the European Union’s Horizon Europe research andinnovation programme under the Marie Skłodowska-Curie 2024 Post-doctoral Fellowship No 101198277 (TopQMat). JS acknowledges fundingfrom the European Union’s Horizon Europe research and innovation pro-gramme under the Marie Skłodowska-Curie grant agreement No101209345-ART.QM funded by the European Union. Views and opinionsexpressed are, however, those of the author(s) only and do not necessarilyre ect those of the European Union or European Research ExecutiveAgency. Neither the European Union nor the granting authority can be heldresponsible for them. This work was funded by the Würzburg-DresdenCluster of Excellence on Complexity, Topology and Dynamics in QuantumMatter - ctd.qmat (EXC 2147, project-id 390858490) and by the DFG throughSFB1170“Tocotronics” and directly via RE 1469/13-2. N.G.E. and D.N. acknowledge nancial support from the project“Podizanje znanstveneizvrsnosti Centra za napredne laserske tehnike (CALTboost)” nanced bythe European Union through the National Recovery and Resilience Plan2021-2026 (NRPP), European Regional Development Fund for the project‘Materials for clean energy, advanced sensors and quantum technologies’(Grant No. PK.1.1.10.0002), and Croatian Science Foundation (Grant no. IP-2025-02-5926). QC also acknowledges support from the TERAQUANTUMproject of the Région Nouvelle-Aquitaine. This work was supported by theTWISTnSHINE, funded as project No. LL2314 by Programme ERC CZ.

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Contributing Institute(s):

1. FS-SXQM (FS-SXQM)

Research Program(s):

1. 632 - Materials – Quantum, Complex and Functional Materials (POF4-632) (POF4-632)
2. DFG project G:(GEPRIS)258499086 - SFB 1170: Topologische und korrelierte Elektronik in Ober- und Grenzflächen ("ToCoTronics") (258499086) (258499086)

Experiment(s):

1. Measurement at external facility

Appears in the scientific report 2026

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