Spin-orbit interaction induced in graphene by transition metal dichalcogenides

Abstract

We report a systematic study on strong enhancement of spin-orbit interaction (SOI) in graphene induced by transition-metal dichalcogenides (TMDs). Low-temperature magnetotoransport measurements of graphene proximitized to different TMDs (monolayer and bulk ${\mathrm{WSe}}_{2},{\mathrm{WS}}_{2}$, and monolayer ${\mathrm{MoS}}_{2})$ all exhibit weak antilocalization peaks, a signature of strong SOI induced in graphene. The amplitudes of the induced SOI are different for different materials and thickness, and we find that monolayer ${\mathrm{WSe}}_{2}$ and ${\mathrm{WS}}_{2}$ can induce much stronger SOI than bulk ${\mathrm{WSe}}_{2},{\mathrm{WS}}_{2}$, and monolayer ${\mathrm{MoS}}_{2}$. The estimated spin-orbit (SO) scattering strength for graphene/monolayer ${\mathrm{WSe}}_{2}$ and graphene/monolayer ${\mathrm{WS}}_{2}$ reaches $\ensuremath{\sim}10$ meV, whereas for graphene/bulk ${\mathrm{WSe}}_{2}$, graphene/bulk ${\mathrm{WS}}_{2}$, and graphene/monolayer ${\mathrm{MoS}}_{2}$, it is around 1 meV or less. We also discuss the symmetry and type of the induced SOI in detail, especially focusing on the identification of intrinsic (Kane-Mele) and valley-Zeeman (VZ) SOI by determining the dominant spin relaxation mechanism. Our findings pave the way for realizing the quantum spin Hall (QSH) state in graphene.