Doppler velocimetry of spin propagation in a two-dimensional electron gas

Controlling the flow of electrons by manipulating their spin is a key to the development of spin-based electronics. Recent demonstrations of electrical-gate control in spin-transistor configurations have shown great promise, but operation at room temperature remains elusive. Further progress requires a deeper understanding of the propagation of spin polarization, particularly in the high-mobility semiconductors used for devices. Here we report the application of Doppler velocimetry to resolve the motion of spin-polarized electrons in GaAs quantum wells driven by a drifting Fermi sea. We find that the spin mobility tracks the high electron mobility precisely as a function of temperature. However, we also observe that the coherent precession of spins driven by spin-orbit interaction, which is essential for the operation of a broad class of spin logic devices, breaks down at temperatures above 150 K, for reasons that are not yet understood theoretically.