# Momentum-Resolved View of Electron-Phonon Coupling in Multilayer WSe$_2$

## TL;DR

This study provides a momentum-resolved understanding of how photoexcited electrons in multilayer WSe$_2$ transfer energy to phonons, revealing detailed dynamics of electron-phonon interactions relevant for nanoscale electronic and thermal applications.

## Contribution

It combines femtosecond electron diffraction and first-principles calculations to map momentum-dependent electron-phonon coupling in WSe$_2$, offering new insights into energy transfer mechanisms.

## Key findings

- Electron relaxation dominated by intervalley scattering and zone-boundary phonon emission.
- Transient non-thermal phonon distributions observed and analyzed.
- Results inform predictions of electrical and thermal transport in TMDCs.

## Abstract

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.