Strain-induced activation of chiral-phonon emission in monolayer WS$_2$

TL;DR

This paper theoretically explores how strain in monolayer WS$_2$ enables control over chiral-phonon emission by altering electron-phonon interactions, revealing new relaxation pathways and dynamical regimes.

Contribution

It demonstrates that strain can induce a transition between different phonon emission regimes, enabling selective activation of chiral phonons in monolayer WS$_2$.

Findings

Strain modifies electron-phonon scattering phase space.

High strain triggers emission of chiral phonons.

Low strain favors linearly-polarized phonons.

Abstract

We report a theoretical investigation of the ultrafast dynamics of electrons and phonons in strained monolayer WS$_2$ following photoexcitation. We show that strain substantially modifies the phase space for electron-phonon scattering, unlocking new relaxation pathways that are unavailable in the pristine monolayer. In particular, strain triggers a transition between distinct dynamical regimes of the non-equilibrium lattice dynamics characterized by the emission of chiral phonons under high strain and linearly-polarized phonons under low strain. For valley-polarized electronic excitations, this mechanism can be exploited to selectively activate the emission of chiral phonons -- phonons carrying a net angular momentum. Our simulations are based on state-of-the-art ab-initio methods and focus exclusively on realistic excitation and strain conditions that have already been achieved in recent experimental studies. Overall, strain emerges as a powerful tool for controlling chiral phonons emission and relaxation pathways in multivalley quantum materials.