Strong Anisotropic Spin-Orbit Interaction Induced in Graphene by Monolayer WS2

We demonstrate strong anisotropic spin-orbit interaction (SOI) in graphene induced by monolayer WS2. Direct comparison between graphene-monolayer WS2 and graphene-bulk WS2 systems in magnetotransport measurements reveals that monolayer transition metal dichalcogenide can induce much stronger SOI than bulk. Detailed theoretical analysis of the weak antilocalization curves gives an estimated spin-orbit energy (E-so) higher than 10 meV. The symmetry of the induced SOI is also discussed, and the dominant z -> -z symmetric SOI can only explain the experimental results. Spin relaxation by the Elliot-Yafet mechanism and anomalous resistance increase with temperature close to the Dirac point indicates KaneMele SOI induced in graphene.