  Space- and time-resolved measurements of spin drift and diffusion are
performed on a GaAs-hosted two-dimensional electron gas. For spins where
forward drift is compensated by backward diffusion, we find a precession
frequency in absence of an external magnetic field. The frequency depends
linearly on the drift velocity and is explained by the cubic Dresselhaus
spin-orbit interaction, for which drift leads to a spin precession angle twice
that of spins that diffuse the same distance.
