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We investigate the Eg phonon dynamics under intense photoexcitation by performing anisotropic transient reflectivity (TR) measurements on a 1-mm thick bismuth single crystal at 11 K. The amplitude of coherent Eg phonon is found to increase with incident pump fluence up to 10 mJ/cm2 and then turns to an apparent decrease. This behavior is in stark contrast to the amplitude of the A1g phonon in standard TR measurements, which increases monotonically up to 20 mJ/cm2 and then saturates. The contrasted behaviors of the two phonon modes can be interpreted in terms of the strong coupling of the Eg oscillation with large-amplitude A1g displacement on a highly excited electronic state, where dynamic fluctuation of the vibrational potential would lead to a quick loss in the Eg vibrational coherence. Unlike the previous studies on thin Bi films on substrates we observe no sign of a transition to a high-symmetry phase but a sign of partial damage of the crystalline surface at 28 mJ/cm2, possibly due to less efficient cooling at the surface of a bulk crystal.

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• In Copyright
  ©2024 American Physical Society

Keyword: coherent phonons, phonon-phonon coupling, bismuth

Date published: 2024-09-20

Publisher: American Physical Society (APS)

Journal:

• PHYSICAL REVIEW B (ISSN: 24699950) vol. 110 issue. 9 094313

Funding:

Manuscript type: Author's version (Accepted manuscript)

MDR DOI: https://doi.org/10.48505/nims.4793

First published URL: https://doi.org/10.1103/physrevb.110.094313

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Updated at: 2024-10-02 16:30:23 +0900

Published on MDR: 2024-10-02 16:30:23 +0900