Ultrafast Dynamics of Electron-phonon Coupling in Transition-metal Dichalcogenides

TL;DR

This study uses femtosecond laser spectroscopy to investigate ultrafast electron-phonon interactions in 2H-MoTe2, revealing long-lived phonons and their dependence on excitation conditions, which impacts electronic transport understanding.

Contribution

It provides new insights into the weak anharmonic phonon-phonon coupling and carrier-density-dependent electron-phonon interactions in 2H-MoTe2.

Findings

Long-lived coherent A1g phonon mode observed at room temperature.

Decay rate decreases with increasing laser fluence.

Phonon softening and reduced decay rate linked to carrier density.

Abstract

Time-domain femtosecond laser spectroscopic measurements of the ultrafast lattice dynamics in 2H-MoTe2 bulk crystals were carried out to understand the carrier-phonon interactions that govern electronic transport properties. An unusually long lifetime coherent A1g phonon mode was observed even in the presence of very large density of photo-excited carriers at room temperature. The decay rate was observed to decrease with increasing excitation laser fluence. Based on the laser fluence dependence including the inducement of significant phonon softening and a peculiar decrease in phonon decay rate, we attribute the long lifetime lattice dynamics to weak anharmonic phonon-phonon coupling and a carrier-density-dependent deformation potential electron-phonon coupling.