  We report the observation of a spin-orbit torque (SOT) originating from the
surface Rashba-Edelstein effect. We found that the SOT in a prototypical
spin-orbitronic system, a Pt/Co bilayer, can be manipulated by molecular
self-assembly on the Pt surface. This evidences that the Rashba spin-orbit
coupling at the Pt surface generates a sizable SOT, which has been 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.
