Spin accumulation and dynamics in inversion-symmetric transition metal dichalcogenides

Transition metal dichalcogenides (TMDs) are fascinating materials for spin-logic devices due to their large spin-orbit coupling and their spin-valley locking. Recently, it has been proposed that optical generation of spin accumulation in inversion symmetric TMDs is possible due to a layer-dependent hidden spin polarization[1,2]. Time-resolved photoemission studies showed that the optically generated spin accumulation in the conduction band of the surface layer of bulk TMD crystals decays very fast, in the order of 100s of fs, due to high scattering rates where the electron loses its layer polarization[3]. By using ultrafast time-resolved Kerr rotation and transient reflectivity experiments in WSe₂ and MoSe₂ we are able to probe the spin and carrier dynamics of the whole crystal and unveil a spin-layer relaxation time of tens of ps at low temperatures, which is reduced, but still sizeable (a few ps) at room temperature. By temperature dependence measurements and comparing the two materials with different spin-orbit coupling strengths we are able to unveil the different spin relaxation mechanisms in inversion-symmetric TMDs.

[1] Zhang at al., Nat. Phys. 10, 387 (2014)
[2] Gong et al., Nat. Comm. 4, 2053 (2013)
[3] Bertoni et al., Phys. Rev. Lett. 117, 277201 (2016)