We investigate the interactions of photoexcited carriers with lattice vibrations in thin films of the layered transition metal dichalcogenide (TMDC) WSe2. 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 Σ 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.
@article{arxiv.1703.03496,
title = {Momentum-Resolved View of Electron-Phonon Coupling in Multilayer WSe$_2$},
author = {Lutz Waldecker and Roman Bertoni and H. Hübener and Thomas Brumme and Thomas Vasileiadis and Daniela Zahn and Angel Rubio and Ralph Ernstorfer},
journal= {arXiv preprint arXiv:1703.03496},
year = {2017}
}