Coupled spin and valley physics in monolayers of MoS2 and other group-VI dichalcogenides

TL;DR

This paper demonstrates how inversion symmetry breaking and spin-orbit coupling in monolayer MoS2 and similar materials enable coupled spin and valley control, leading to novel effects like valley Hall and spin Hall, with potential for integrated valleytronics and spintronics.

Contribution

It reveals the coupled spin-valley physics in monolayer group-VI dichalcogenides and explores their implications for controlling spin and valley degrees of freedom.

Findings

Spin-valley coupling suppresses relaxation of spin and valley indices.

Valley Hall and spin Hall effects coexist in doped systems.

Optical transitions allow selective excitation of spin-valley states.

Abstract

We show that inversion symmetry breaking together with spin-orbit coupling leads to coupled spin and valley physics in monolayers of MoS2 and other group-VI dichalcogenides, making possible controls of spin and valley in these 2D materials. The spin-valley coupling at the valence band edges suppresses spin and valley relaxation, as flip of each index alone is forbidden by the valley contrasting spin splitting. Valley Hall and spin Hall effects coexist in both electron-doped and hole-doped systems. Optical interband transitions have frequency-dependent polarization selection rules which allow selective photoexcitation of carriers with various combination of valley and spin indices. Photo-induced spin Hall and valley Hall effects can generate long lived spin and valley accumulations on sample boundaries. The physics discussed here provides a route towards the integration of valleytronics and spintronics in multi-valley materials with strong spin-orbit coupling and inversion symmetry breaking.