Symmetry and Control of Spin-Scattering Processes in Two-Dimensional Transition Metal Dichalcogenides

TL;DR

This paper uses symmetry analysis to understand and control spin scattering mechanisms in monolayer and bilayer transition metal dichalcogenides, revealing how symmetry and external fields influence spin lifetimes in these materials.

Contribution

It provides a symmetry-based framework to identify spin scattering processes and demonstrates how external electric fields can control spin lifetimes in TMDs.

Findings

Distinct spin-scattering mechanisms in monolayer and bilayer TMDs.

Partial protection of certain electronic states by time-reversal symmetry.

Electrical control of spin lifetime via out-of-plane electric fields.

Abstract

Transition metal dichalcogenides (TMDs) combine interesting optical and spintronic properties in an atomically-thin material, where the light polarization can be used to control the spin and valley degrees-of-freedom for the development of novel opto-spintronic devices. These promising properties emerge due to their large spin-orbit coupling in combination with their crystal symmetries. Here, we provide simple symmetry arguments in a group-theory approach to unveil the symmetry-allowed spin scattering mechanisms, and indicate how one can use these concepts towards an external control of the spin lifetime. We perform this analysis for both monolayer (inversion asymmetric) and bilayer (inversion symmetric) crystals, indicating the different mechanisms that play a role in these systems. We show that, in monolayer TMDs, electrons and holes transform fundamentally differently -- leading to distinct spin-scattering processes. We find that one of the electronic states in the conduction band is partially protected by time-reversal symmetry, indicating a longer spin lifetime for that state. In bilayer and bulk TMDs, a hidden spin-polarization can exist within each layer despite the presence of global inversion symmetry. We show that this feature enables control of the interlayer spin-flipping scattering processes via an out-of-plane electric field, providing a mechanism for electrical control of the spin lifetime.