Surface Rashba-Edelstein Spin-Orbit Torque Revealed by Molecular Self-Assembly

We report the observation of a spin-orbit torque (SOT) originating from the surface Rashba-Edelstein effect. We find that the SOT in a prototypical spin-orbitronic system, a $\mathrm{Pt}$/$\mathrm{Co}$ bilayer, can be manipulated by molecular self-assembly on the $\mathrm{Pt}$ surface. This provides evidence that the Rashba spin-orbit coupling at the $\mathrm{Pt}$ surface generates a sizable SOT, which is hidden by the strong bulk and interface spin-orbit coupling. We show that the molecular tuning of the surface Rashba-Edelstein SOT is consistent with density-functional-theory calculations. These results illustrate the crucial role of the surface spin-orbit coupling in the SOT generation, which alters the landscape of metallic spin-orbitronic devices.