A Momentum-Resolved View on Electron-Phonon Coupling in Multilayer WSe 2

Physical Review Letters 119, 036803 (2017)

A Momentum-Resolved View on Electron-Phonon Coupling in Multilayer WSe 2

Lutz Waldecker, Roman Bertoni, H. Hübener, Thomas Brumme, Thomas Vasileiadis, Daniela Zahn, Angel Rubio, Ralph Ernstorfer

We investigate the interactions of photoexcited carriers with lattice vibrations in thin films of the layered transition metal dichalcogenide (TMDC) WSe$_2$. Employing femtosecond electron diffraction with monocrystalline samples and first principle density functional theory calculations, we obtain a momentum-resolved picture of the energy-transfer from excited electrons to phonons. The measured momentum-dependent phonon population dynamics are compared to first principle calculations of the phonon linewidth and can be rationalized in terms of electronic phase-space arguments. The relaxation of excited states in the conduction band is dominated by intervalley scattering between $\Sigma$ valleys and the emission of zone-boundary phonons. Transiently, the momentum-dependent electron-phonon coupling leads to a non-thermal phonon distribution, which, on longer timescales, relaxes to a thermal distribution via electron-phonon and phonon-phonon collisions. Our results constitute a basis for monitoring and predicting out of equilibrium electrical and thermal transport properties for nanoscale applications of TMDCs.

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This project has received funding from the Max Planck Society and from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement numbers ERC-2015-CoG-682843 and ERC-2015-AdG- 694097). R.B. thanks the Alexander von Humboldt foundation for financial support. H.H. acknowledges support from the People Programme (Marie Curie Actions) of the European Union’s Seventh Framework Programme FP7-PEOPLE-2013-IEF project No. 622934. We acknowledges financial support from Grupos Consolidados (IT578-13) and Air Force Office of Scientific Research Award (Grant No. FA2386-15-1-0006 AOARD 144088).

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