Electrical spin generation by the spin Hall effect in semiconductors

Electrical generation of spin polarization by the spin Hall effect is imaged with both spatial and temporal resolution using Kerr rotation microscopy in bulk zincblende semiconductors. The spin Hall effect, which arises due to the spin-orbit coupling, refers to the generation of a pure spin current transverse to a charge current driven by an electric field which causes a spontaneous quasi-equilibrium spin accumulation near sample boundaries without the need for magnetic fields or magnetic materials. Bulk current-induced in-plane spin polarization and out-of-plane spin accumulation from the spin Hall effect are observed in the II-VI semiconductor ZnSe despite no evidence for a spin-orbit induced internal magnetic field, which are only observed sub-critical thickness ZnSe with enhanced k-linear Hamiltonian terms due to biaxial strain. The wide band gap of ZnSe enables the first observation of electrical spin generation at room temperature. The spatial dependence of steady-state spin accumulation from the spin Hall effect is addressed in channels made of the III-V semiconductor GaAs. One- and two-dimensional spatially-resolved diffusion modeling clarifies the important role of drift and diffusion in transporting spin generated at sample boundaries to the interior of the device. Driving spin accumulation with an electrical pulse and probing with a frequency-synchronized ultrafast laser enables time-resolved measurement of the spin Hall effect. Probing the dynamical processes of spin accumulation and diffusion reveals spatially-dependent nanosecond timescales comparable to the electric-field dependent spin coherence time. Prospects are considered for an all-electrical measurement of the spin Hall effect which should enable more accurate determination of the magnitude of the spin Hall conductivity and illuminate the microscopic mechanisms governing the spin Hall effect in GaAs.