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Journal article
Ultrafast dynamics in the high-symmetry and in the charge density wave phase of 2H-NbSe2
Physical review. B, v 102(20)
30 Nov 2020
Abstract
We investigate carrier and collective mode dynamics in 2H-NbSe2 using time-resolved optical pump-probe spectroscopy and compare the results with first-principles calculations. Broadband ultrafast reflectivity studies of 2H-NbSe2 in a wide temperature interval covering the normal, charge density wave (CDW) and superconducting phase were performed. Spectral features observed in the transient reflectivity experiment were associated with specific optical transitions obtained from band structure calculations. Displacive excitation of coherent phonons showed CDW-associated coherent oscillations of the soft phonon mode across the whole spectral range. Temperature evolution of this coherent phonon mode in the low-excitation linear regime shows softening of the mode down to the CDW transition temperature T-CDW with subsequent hardening below T-CDW. The global fit of the broadband probe data reveals four different relaxation times associated with characteristic electron-electron, electron-phonon, and phonon-phonon relaxation processes. From first-principles calculations of electron-phonon coupling we associate the few picosecond electron-phonon relaxation time tau(2) with a specific group of phonons with frequencies around 20 meV. On the other hand, the anomalously long relaxation time of tau(3) similar to 100 ps is associated with anharmonicity-driven phonon-phonon scattering. All relaxation processes result from anomalies near the second order CDW phase transition that are reflected in the temperature dependencies of the characteristic relaxation times and amplitudes of coherent oscillations. At the highest fluences we observe electronic melting of the CDW and disappearance of the mode hardening below T-CDW.
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Details
- Title
- Ultrafast dynamics in the high-symmetry and in the charge density wave phase of 2H-NbSe2
- Creators
- A. Anikin - Drexel UniversityR. D. Schaller - Argonne National LaboratoryG. P. Wiederrecht - Argonne National LaboratoryE. R. Margine - Binghamton UniversityI. I. Mazin - George Mason UniversityG. Karapetrov - Drexel UniversityArgonne National Lab. (ANL), Argonne, IL (United States). Center for Nanoscale Materials
- Publication Details
- Physical review. B, v 102(20)
- Publisher
- Amer Physical Soc
- Number of pages
- 10
- Grant note
- DE-SC0012575 / Center for Complex Materials from First Principles, an Energy Frontier Research Center - US Department of Energy, Office of Science, Basic Energy Sciences; United States Department of Energy (DOE) N00014-20-1-2345 / ONR; Office of Naval Research DE-AC02-06CH11357 / US Department of Energy, Office of Science, Office of Basic Energy Sciences; United States Department of Energy (DOE) ACI-1548562; ECCS-1711015; OAC-1740263 / National Science Foundation; National Science Foundation (NSF)
- Resource Type
- Journal article
- Language
- English
- Academic Unit
- Physics
- Web of Science ID
- WOS:000594089300010
- Scopus ID
- 2-s2.0-85097191089
- Other Identifier
- 991019168984304721
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Data related to this publication, from InCites Benchmarking & Analytics tool:
- Collaboration types
- Domestic collaboration
- Web of Science research areas
- Materials Science, Multidisciplinary
- Physics, Applied
- Physics, Condensed Matter