Nonequilibrium Lattice Dynamics in Monolayer MoS2

TL;DR

This study explores the nonequilibrium behavior of electrons and phonons in monolayer MoS2 using first-principles calculations and the Boltzmann equation, revealing momentum-dependent phonon emission and anisotropic phonon populations that persist for several picoseconds.

Contribution

It introduces a detailed first-principles approach to understanding coupled electron-phonon dynamics in 2D materials, highlighting momentum constraints and anisotropic phonon populations.

Findings

Electron-phonon scattering is restricted to high-symmetry points in the Brillouin zone.

Anisotropic phonon populations persist for up to 10 ps before thermalization.

Momentum selectivity influences the decay pathways of excited carriers.

Abstract

The coupled nonequilibrium dynamics of electrons and phonons in monolayer MoS2 is investigated by combining first-principles calculations of the electron-phonon and phonon-phonon interaction with the time-dependent Boltzmann equation. Strict phase-space constraints in the electron-phonon scattering are found to influence profoundly the decay path of excited electrons and holes, restricting the emission of phonons to crystal momenta close to few high-symmetry points in the Brillouin zone. As a result of momentum selectivity in the phonon emission, the nonequilibrium lattice dynamics is characterized by the emergence of a highly-anisotropic population of phonons in reciprocal space, which persists for up to 10 ps until thermal equilibrium is restored by phonon-phonon scattering. Achieving control of the nonequilibrium dynamics of the lattice may provide unexplored opportunities to selectively enhance the phonon population of two-dimensional crystals and, thereby, transiently tailor electron-phonon interactions over sub-picosecond time scales.