Electron-Phonon Coupling and Energy Flow in a Simple Metal beyond the Two-Temperature Approximation
The electron-phonon coupling and the corresponding energy exchange are investigated experimentally and by ab initio theory in nonequilibrium states of the free-electron metal aluminium. The temporal evolution of the atomic mean-squared displacement in laser-excited thin freestanding films is monitor...
| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
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American Physical Society
2016-04-01
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| Series: | Physical Review X |
| Online Access: | http://doi.org/10.1103/PhysRevX.6.021003 |
| _version_ | 1818730671774892032 |
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| author | Lutz Waldecker Roman Bertoni Ralph Ernstorfer Jan Vorberger |
| author_facet | Lutz Waldecker Roman Bertoni Ralph Ernstorfer Jan Vorberger |
| author_sort | Lutz Waldecker |
| collection | DOAJ |
| description | The electron-phonon coupling and the corresponding energy exchange are investigated experimentally and by ab initio theory in nonequilibrium states of the free-electron metal aluminium. The temporal evolution of the atomic mean-squared displacement in laser-excited thin freestanding films is monitored by femtosecond electron diffraction. The electron-phonon coupling strength is obtained for a range of electronic and lattice temperatures from density functional theory molecular dynamics simulations. The electron-phonon coupling parameter extracted from the experimental data in the framework of a two-temperature model (TTM) deviates significantly from the ab initio values. We introduce a nonthermal lattice model (NLM) for describing nonthermal phonon distributions as a sum of thermal distributions of the three phonon branches. The contributions of individual phonon branches to the electron-phonon coupling are considered independently and found to be dominated by longitudinal acoustic phonons. Using all material parameters from first-principles calculations except the phonon-phonon coupling strength, the prediction of the energy transfer from electrons to phonons by the NLM is in excellent agreement with time-resolved diffraction data. Our results suggest that the TTM is insufficient for describing the microscopic energy flow even for simple metals like aluminium and that the determination of the electron-phonon coupling constant from time-resolved experiments by means of the TTM leads to incorrect values. In contrast, the NLM describing transient phonon populations by three parameters appears to be a sufficient model for quantitatively describing electron-lattice equilibration in aluminium. We discuss the general applicability of the NLM and provide a criterion for the suitability of the two-temperature approximation for other metals. |
| first_indexed | 2024-12-17T23:05:30Z |
| format | Article |
| id | doaj.art-87151b639cea41c4a70bef43588738ef |
| institution | Directory Open Access Journal |
| issn | 2160-3308 |
| language | English |
| last_indexed | 2024-12-17T23:05:30Z |
| publishDate | 2016-04-01 |
| publisher | American Physical Society |
| record_format | Article |
| series | Physical Review X |
| spelling | doaj.art-87151b639cea41c4a70bef43588738ef2022-12-21T21:29:17ZengAmerican Physical SocietyPhysical Review X2160-33082016-04-016202100310.1103/PhysRevX.6.021003Electron-Phonon Coupling and Energy Flow in a Simple Metal beyond the Two-Temperature ApproximationLutz WaldeckerRoman BertoniRalph ErnstorferJan VorbergerThe electron-phonon coupling and the corresponding energy exchange are investigated experimentally and by ab initio theory in nonequilibrium states of the free-electron metal aluminium. The temporal evolution of the atomic mean-squared displacement in laser-excited thin freestanding films is monitored by femtosecond electron diffraction. The electron-phonon coupling strength is obtained for a range of electronic and lattice temperatures from density functional theory molecular dynamics simulations. The electron-phonon coupling parameter extracted from the experimental data in the framework of a two-temperature model (TTM) deviates significantly from the ab initio values. We introduce a nonthermal lattice model (NLM) for describing nonthermal phonon distributions as a sum of thermal distributions of the three phonon branches. The contributions of individual phonon branches to the electron-phonon coupling are considered independently and found to be dominated by longitudinal acoustic phonons. Using all material parameters from first-principles calculations except the phonon-phonon coupling strength, the prediction of the energy transfer from electrons to phonons by the NLM is in excellent agreement with time-resolved diffraction data. Our results suggest that the TTM is insufficient for describing the microscopic energy flow even for simple metals like aluminium and that the determination of the electron-phonon coupling constant from time-resolved experiments by means of the TTM leads to incorrect values. In contrast, the NLM describing transient phonon populations by three parameters appears to be a sufficient model for quantitatively describing electron-lattice equilibration in aluminium. We discuss the general applicability of the NLM and provide a criterion for the suitability of the two-temperature approximation for other metals.http://doi.org/10.1103/PhysRevX.6.021003 |
| spellingShingle | Lutz Waldecker Roman Bertoni Ralph Ernstorfer Jan Vorberger Electron-Phonon Coupling and Energy Flow in a Simple Metal beyond the Two-Temperature Approximation Physical Review X |
| title | Electron-Phonon Coupling and Energy Flow in a Simple Metal beyond the Two-Temperature Approximation |
| title_full | Electron-Phonon Coupling and Energy Flow in a Simple Metal beyond the Two-Temperature Approximation |
| title_fullStr | Electron-Phonon Coupling and Energy Flow in a Simple Metal beyond the Two-Temperature Approximation |
| title_full_unstemmed | Electron-Phonon Coupling and Energy Flow in a Simple Metal beyond the Two-Temperature Approximation |
| title_short | Electron-Phonon Coupling and Energy Flow in a Simple Metal beyond the Two-Temperature Approximation |
| title_sort | electron phonon coupling and energy flow in a simple metal beyond the two temperature approximation |
| url | http://doi.org/10.1103/PhysRevX.6.021003 |
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