Electrical resistance associated with the scattering of optically oriented spin-polarized electrons in $n$-GaAs

In a bulk GaAs crystal, an unusual magnetoresistance effect, which takes place when a spin-polarized current flows through the sample, was detected. Under conditions of optical pumping of electron spins, an external magnetic field directed along the electric current and perpendicular to the oriented spins decreases the resistance of the material. The phenomenon is due to the spin-dependent scattering of electrons by neutral donors. It was found that the sign of the magnetoresistance does not depend on the sign of the exciting light circular polarization; the effect is even with respect to the sign of the spin polarization of the carriers. The effect is absent when the excitation is linear polarized, which indicates a correlation between the spins of optically oriented free electrons and electrons localized on donors.