  Spin relaxation can be greatly enhanced in narrow channels of two-dimensional
electron gas due to ballistic spin resonance, which is mediated by spin-orbit
interaction for trajectories that bounce rapidly between channel walls. The
channel orientation determines which momenta affect the relaxation process, so
comparing relaxation for two orientations provides a direct determination of
spin-orbit anisotropy. Electrical measurements of pure spin currents are shown
to reveal an order of magnitude stronger relaxation for channels fabricated
along the [110] crystal axis in a GaAs electron gas compared to [-110]
channels, believed to result from interference between structural and bulk
inversion asymmetries.
