Issue 21, 2024

Multiple coherent amplitude modes and exciton–phonon coupling in quasi-one-dimensional excitonic insulator Ta2NiSe5

Abstract

An excitonic insulator (EI) is an intriguing correlated electronic phase of condensed excitons. Ta2NiSe5 is a model material for investigating condensed excitonic states. Herein, femtosecond pump–probe spectroscopy is used to study the coherent phonon dynamics and associated exciton–phonon coupling in single-crystal Ta2NiSe5. The reflectivity time series consists of exponential decay due to hot carriers and damped oscillations due to the Ag phonon vibration. Given the in-plane anisotropic thermal conductivity of Ta2NiSe5, coherent phonon oscillations are stronger with perpendicular polarization to its quasi-one-dimensional chains. The 1-, 2-, and 4-THz vibration modes show coherent amplitude responses in the EI phase of Ta2NiSe5 with increasing temperature, totally different from those of normal coherent phonons (the 3- and 3.7-THz modes). The amplitude modes at higher frequencies decouple with the EI order parameter at lower temperatures, as supported by theoretical analysis with a model Hamiltonian of the exciton–phonon coupling system. Our work provides valuable insights into the character of the EI order parameter and its coupling to multiple coherent amplitude modes.

Graphical abstract: Multiple coherent amplitude modes and exciton–phonon coupling in quasi-one-dimensional excitonic insulator Ta2NiSe5

Supplementary files

Article information

Article type
Paper
Submitted
19 Jan 2024
Accepted
29 Apr 2024
First published
15 May 2024

Phys. Chem. Chem. Phys., 2024,26, 15417-15425

Multiple coherent amplitude modes and exciton–phonon coupling in quasi-one-dimensional excitonic insulator Ta2NiSe5

Y. Jiang, Y. Mi, J. Guo, Z. Wang, N. Zhang, B. Liu and S. Luo, Phys. Chem. Chem. Phys., 2024, 26, 15417 DOI: 10.1039/D4CP00261J

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