Spectrally Resolving the Phase and Amplitude of Coherent Phonons in the Charge Density Wave State of 1T-TaSe2

Enrico Da Como

doi:10.1002/adom.202200362

Spectrally Resolving the Phase and Amplitude of Coherent Phonons in the Charge Density Wave State of 1T-TaSe2

Enrico Da Como

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6 Citations (SciVal)

Abstract

The excitation and detection of coherent phonons have given unique insights into the condensed matter, in particular for materials with strong electron–phonon coupling. A study of coherent phonons is reported in the layered charge density wave (CDW) compound 1T-TaSe ₂ performed using transient broadband reflectivity spectroscopy, in the photon energy range 1.75–2.65 eV. Several intense and long-lasting (>20 ps) oscillations, arising from the CDW superlattice reconstruction, are observed allowing for detailed analysis of the spectral dependence of their amplitude and phase. For energies above 2.4 eV, where transitions involve Ta d-bands, the CDW amplitude mode at 2.19 THz is found to dominate the coherent response. At lower energies, instead, beating arises between additional frequencies, with a particularly intense mode at 2.95 THz. Interestingly, the spectral analysis reveals a π phase shift at 2.4 eV. Results are discussed considering the selective coupling of specific modes to energy bands involved in the optical transitions seen in steady-state reflectivity. The work demonstrates how coherent phonon spectroscopy can distinguish and resolve optical states strongly coupled to the CDW order and provide additional information normally hidden in conventional steady-state techniques.

Original language	English
Article number	2200362
Journal	Advanced Optical Materials
Volume	10
Issue number	14
Early online date	17 Jun 2022
DOIs	https://doi.org/10.1002/adom.202200362
Publication status	Published - 18 Jul 2022

Bibliographical note

Funding Information:
Computational work was performed on the University of Bath's High-Performance Computing Facility and was also supported by the University of Bath Cloud Pilot Project. Support for this work was provided by EPSRC grant EP/L015544. E.C. acknowledges funding from Italian PRIN project 2017BZPKSZ. The authors also wish to thank the Royal Society for support under the Wolfson Laboratory Refurbishment scheme. The authors appreciate the technical support by Phil Jones, Ash Moore, and Clare Cambridge at University of Bath.

Publisher Copyright:
© 2022 The Authors. Advanced Optical Materials published by Wiley-VCH GmbH.

Keywords

TaSe
charge density waves
coherent phonons
transition metal dichalcogenides
ultrafast spectroscopy

ASJC Scopus subject areas

Electronic, Optical and Magnetic Materials
Atomic and Molecular Physics, and Optics

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10.1002/adom.202200362Licence: CC BY

Cite this

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title = "Spectrally Resolving the Phase and Amplitude of Coherent Phonons in the Charge Density Wave State of 1T-TaSe2",

abstract = "The excitation and detection of coherent phonons have given unique insights into the condensed matter, in particular for materials with strong electron–phonon coupling. A study of coherent phonons is reported in the layered charge density wave (CDW) compound 1T-TaSe 2 performed using transient broadband reflectivity spectroscopy, in the photon energy range 1.75–2.65 eV. Several intense and long-lasting (>20 ps) oscillations, arising from the CDW superlattice reconstruction, are observed allowing for detailed analysis of the spectral dependence of their amplitude and phase. For energies above 2.4 eV, where transitions involve Ta d-bands, the CDW amplitude mode at 2.19 THz is found to dominate the coherent response. At lower energies, instead, beating arises between additional frequencies, with a particularly intense mode at 2.95 THz. Interestingly, the spectral analysis reveals a π phase shift at 2.4 eV. Results are discussed considering the selective coupling of specific modes to energy bands involved in the optical transitions seen in steady-state reflectivity. The work demonstrates how coherent phonon spectroscopy can distinguish and resolve optical states strongly coupled to the CDW order and provide additional information normally hidden in conventional steady-state techniques. ",

keywords = "TaSe, charge density waves, coherent phonons, transition metal dichalcogenides, ultrafast spectroscopy",

author = "{Da Como}, Enrico",

note = "Funding Information: Computational work was performed on the University of Bath's High-Performance Computing Facility and was also supported by the University of Bath Cloud Pilot Project. Support for this work was provided by EPSRC grant EP/L015544. E.C. acknowledges funding from Italian PRIN project 2017BZPKSZ. The authors also wish to thank the Royal Society for support under the Wolfson Laboratory Refurbishment scheme. The authors appreciate the technical support by Phil Jones, Ash Moore, and Clare Cambridge at University of Bath. Publisher Copyright: {\textcopyright} 2022 The Authors. Advanced Optical Materials published by Wiley-VCH GmbH.",

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N1 - Funding Information: Computational work was performed on the University of Bath's High-Performance Computing Facility and was also supported by the University of Bath Cloud Pilot Project. Support for this work was provided by EPSRC grant EP/L015544. E.C. acknowledges funding from Italian PRIN project 2017BZPKSZ. The authors also wish to thank the Royal Society for support under the Wolfson Laboratory Refurbishment scheme. The authors appreciate the technical support by Phil Jones, Ash Moore, and Clare Cambridge at University of Bath. Publisher Copyright: © 2022 The Authors. Advanced Optical Materials published by Wiley-VCH GmbH.

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N2 - The excitation and detection of coherent phonons have given unique insights into the condensed matter, in particular for materials with strong electron–phonon coupling. A study of coherent phonons is reported in the layered charge density wave (CDW) compound 1T-TaSe 2 performed using transient broadband reflectivity spectroscopy, in the photon energy range 1.75–2.65 eV. Several intense and long-lasting (>20 ps) oscillations, arising from the CDW superlattice reconstruction, are observed allowing for detailed analysis of the spectral dependence of their amplitude and phase. For energies above 2.4 eV, where transitions involve Ta d-bands, the CDW amplitude mode at 2.19 THz is found to dominate the coherent response. At lower energies, instead, beating arises between additional frequencies, with a particularly intense mode at 2.95 THz. Interestingly, the spectral analysis reveals a π phase shift at 2.4 eV. Results are discussed considering the selective coupling of specific modes to energy bands involved in the optical transitions seen in steady-state reflectivity. The work demonstrates how coherent phonon spectroscopy can distinguish and resolve optical states strongly coupled to the CDW order and provide additional information normally hidden in conventional steady-state techniques.

AB - The excitation and detection of coherent phonons have given unique insights into the condensed matter, in particular for materials with strong electron–phonon coupling. A study of coherent phonons is reported in the layered charge density wave (CDW) compound 1T-TaSe 2 performed using transient broadband reflectivity spectroscopy, in the photon energy range 1.75–2.65 eV. Several intense and long-lasting (>20 ps) oscillations, arising from the CDW superlattice reconstruction, are observed allowing for detailed analysis of the spectral dependence of their amplitude and phase. For energies above 2.4 eV, where transitions involve Ta d-bands, the CDW amplitude mode at 2.19 THz is found to dominate the coherent response. At lower energies, instead, beating arises between additional frequencies, with a particularly intense mode at 2.95 THz. Interestingly, the spectral analysis reveals a π phase shift at 2.4 eV. Results are discussed considering the selective coupling of specific modes to energy bands involved in the optical transitions seen in steady-state reflectivity. The work demonstrates how coherent phonon spectroscopy can distinguish and resolve optical states strongly coupled to the CDW order and provide additional information normally hidden in conventional steady-state techniques.

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Spectrally Resolving the Phase and Amplitude of Coherent Phonons in the Charge Density Wave State of 1T-TaSe2

Abstract

Bibliographical note

Keywords

ASJC Scopus subject areas

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