Efficient Electron Spin Relaxation by Chiral Phonons in WSe$_2$ Monolayers

TL;DR

This paper demonstrates that chiral phonons in WSe$_2$ monolayers facilitate rapid intra-valley electron spin relaxation, with a spin relaxation time around 10 ps, revealing new insights into spin dynamics in 2D materials.

Contribution

It provides the first experimental and theoretical evidence linking chiral phonons to efficient intra-valley spin relaxation in WSe$_2$ monolayers.

Findings

Spin relaxation time is approximately 10 ps.

Chiral phonons enable efficient intra-valley spin relaxation.

Fast electron transfer from bright to dark excitons observed.

Abstract

In transition metal dichalcogenide semiconductor monolayers the spin dynamics of electrons is controlled by the original spin-valley locking effect resulting from the interplay between spin-orbit interaction and inversion asymmetry. As a consequence, for electrons occupying bottom conduction bands, a carrier spin flip occurs only if there is a simultaneous change of valley. However, very little is known about the intra-valley spin relaxation processes. In this work we have performed stationary and time-resolved photoluminescence measurements in high quality WSe$_2$ monolayers. Our experiments highlight an efficient relaxation from bright to dark excitons, due to a fast intra-valley electron transfer from the top to the bottom conduction band with opposite spins. A combination of experiments and theoretical analysis allows us to infer a spin relaxation time of about $\tau_s\sim10~$ps, driven by the interplay between $\Gamma$-valley chiral phonons and spin-orbit mixing.