Imaging Drift and Diffusion of Accumulation from the Spin Hall Effect*

The spontaneous generation of spin polarization near sample edges by the spin Hall effect when electron currents flow in a metal or semiconductor with spin-orbit coupling has attracted recent attention due to the elegant and complex spin-orbit physics as well as the potential for all-electrical spin generation in spintronics devices. Optical techniques in semiconductors allow for spatial resolution of the electrically generated spin accumulation, a feature not present in all-electrical measurements. We use Kerr rotation microscopy to image the spatial and temporal evolution of spin accumulation produced by the extrinsic spin Hall effect in n-GaAs devices. Measurements in a variety of device geometries, including arms transverse to a channel, reveal the unambiguous contribution of longitudinal spin drift in accumulation profiles\footnote{N. P. Stern, D. W. Steuerman, S. Mack, A.C. Gossard, and D. D. Awschalom, \textit{Appl. Phys. Rev. Lett.} \textbf{91}, 062109 (2007)}. We develop one- and two- dimensional drift-diffusion modeling to explain the observed features, providing a more complete understanding of observations of spin accumulation and the spin Hall effect.