Pressure-Induced Exciton States Mediate Coherent Phonon Dynamics in Ta <sub>2</sub> NiSe <sub>5</sub>

Ta<sub>2</sub>NiSe<sub>5</sub> is a room-temperature excitonic insulator (EI) with strong electron-phonon coupling. However, the evolution of this coupling across the phase transition remains elusive. Here we investigated the nonequilibrium dynamics of Ta<sub>2</sub>NiSe<sub>5</sub> under pressure using time-resolved reflectance spectroscopy (TRS). Below 1 GPa, the 2 THz order-parameter-coupled coherent phonon (OPCCP) exhibits an extended coherence lifetime, which indicates the protection of the exciton condensate and is consistent with the rapid recovery of the EI phase. In contrast, the onset of the OPCCP is delayed at higher pressures due to inefficient energy transfer mediated by preformed excitons. Furthermore, the presence of quasi-elastic scattering in Raman spectra and the enhancement of the 2 THz mode asymmetry factor 1/|<i>q</i>| suggest that the system enters a preformed exciton-dominated regime at higher pressures. This study reveals the regulatory effects of different exciton states on coherent phonons.

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Publication Details

Journal
Nano Letters
Published
2026-03-09
DOI
https://doi.org/10.1021/acs.nanolett.6c00090
Primary Topic
2D Materials and Applications
Type
article
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article

Pressure-Induced Exciton States Mediate Coherent Phonon Dynamics in Ta 2 NiSe 5

Guangming Niu, Yun Zhang, Xin Zeng, Jutao Jiang et al.
Nano Letters
2D Materials and Applications
article

Pressure-Induced Exciton States Mediate Coherent Phonon Dynamics in Ta 2 NiSe 5

Guangming Niu, Yun Zhang, Xin Zeng, Jutao Jiang, Kaijun Yuan, Laizhi Sui, Guorong Wu, Xueming Yang, Xiaowei Wang, MengYao Cai, Xin Liu
article en

Abstract

Ta<sub>2</sub>NiSe<sub>5</sub> is a room-temperature excitonic insulator (EI) with strong electron-phonon coupling. However, the evolution of this coupling across the phase transition remains elusive. Here we investigated the nonequilibrium dynamics of Ta<sub>2</sub>NiSe<sub>5</sub> under pressure using time-resolved reflectance spectroscopy (TRS). Below 1 GPa, the 2 THz order-parameter-coupled coherent phonon (OPCCP) exhibits an extended coherence lifetime, which indicates the protection of the exciton condensate and is consistent with the rapid recovery of the EI phase. In contrast, the onset of the OPCCP is delayed at higher pressures due to inefficient energy transfer mediated by preformed excitons. Furthermore, the presence of quasi-elastic scattering in Raman spectra and the enhancement of the 2 THz mode asymmetry factor 1/|<i>q</i>| suggest that the system enters a preformed exciton-dominated regime at higher pressures. This study reveals the regulatory effects of different exciton states on coherent phonons.

Nano LettersVol. 26(11)
Ningbo University of Technology (CN), Dalian Institute of Chemical Physics (CN), Jilin University (CN), Southern University of Science and Technology (CN), Hefei University (CN), Primary Source (US), Jilin Medical University (CN), University of Chinese Academy of Sciences (CN), Dalian Maritime University (CN)
Affordable and clean energy
Openalex Percentile: Top 30%
2D Materials and Applications
DOISourceOpenAlex
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Pressure-Induced Exciton States Mediate Coherent Phonon Dynamics in Ta <sub>2</sub> NiSe <sub>5</sub> — Guangming Niu, Yun Zhang, et al. · Nano Letters (2026) | TGRS Research Map | TGRS