Identification of soft modes across the commensurate-to-incommensurate charge density wave transition in 1$T$-TaSe$_2$
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arXiv
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| Main Authors: | , , , , , |
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| Format: | Preprint |
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2024
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| _version_ | 1866910664629420032 |
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| author | Ruggeri, M. Wolverson, D. Romano, V. Cerullo, G. Sayers, C. J. D'Angelo, G. |
| author_facet | Ruggeri, M. Wolverson, D. Romano, V. Cerullo, G. Sayers, C. J. D'Angelo, G. |
| contents | 1$T$-TaSe$_2$ is a prototypical charge density wave (CDW) material for which electron-phonon coupling and associated lattice distortion play an important role in driving and stabilizing the CDW phase. Here, we investigate the lattice dynamics of bulk 1$T$-TaSe$_2$ using angle-resolved ultralow wavenumber Raman spectroscopy down to 10 cm$^{-1}$. Our high-resolution spectra allow us to identify at least 27 Raman-active modes in the commensurate (CCDW) phase. Contrary to other layered materials, we do not find evidence of interlayer breathing or shear modes, suggestive of $AA$ stacking in the bulk, or sufficiently weak interlayer coupling. Polarization dependence of the mode intensities allows the assignment of their symmetry, which is supported by first-principles calculations of the phonons for the bulk structure using density functional theory. A detailed temperature dependence in the range $T$ = 80 - 500 K allows us to identify soft modes associated with the CDW superlattice. Upon entering the incommensurate (ICCDW) phase above 473 K, we observe a dramatic loss of resolution of all modes, and significant linewidth broadening associated with a reduced phonon lifetime as the charge-order becomes incommensurate with the lattice. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2405_12373 |
| institution | arXiv |
| publishDate | 2024 |
| record_format | arxiv |
| spellingShingle | Identification of soft modes across the commensurate-to-incommensurate charge density wave transition in 1$T$-TaSe$_2$ Ruggeri, M. Wolverson, D. Romano, V. Cerullo, G. Sayers, C. J. D'Angelo, G. Strongly Correlated Electrons 1$T$-TaSe$_2$ is a prototypical charge density wave (CDW) material for which electron-phonon coupling and associated lattice distortion play an important role in driving and stabilizing the CDW phase. Here, we investigate the lattice dynamics of bulk 1$T$-TaSe$_2$ using angle-resolved ultralow wavenumber Raman spectroscopy down to 10 cm$^{-1}$. Our high-resolution spectra allow us to identify at least 27 Raman-active modes in the commensurate (CCDW) phase. Contrary to other layered materials, we do not find evidence of interlayer breathing or shear modes, suggestive of $AA$ stacking in the bulk, or sufficiently weak interlayer coupling. Polarization dependence of the mode intensities allows the assignment of their symmetry, which is supported by first-principles calculations of the phonons for the bulk structure using density functional theory. A detailed temperature dependence in the range $T$ = 80 - 500 K allows us to identify soft modes associated with the CDW superlattice. Upon entering the incommensurate (ICCDW) phase above 473 K, we observe a dramatic loss of resolution of all modes, and significant linewidth broadening associated with a reduced phonon lifetime as the charge-order becomes incommensurate with the lattice. |
| title | Identification of soft modes across the commensurate-to-incommensurate charge density wave transition in 1$T$-TaSe$_2$ |
| topic | Strongly Correlated Electrons |
| url | https://arxiv.org/abs/2405.12373 |