Conversion of spin into directed electric current in quantum wells

A nonequilibrium population of spin-up and spin-down states in quantum well structures has been achieved applying circularly polarized radiation. The spin polarization results in a directed motion of free carriers in the plan e of a quantum well perpendicular to the direction of light propagation. Be cause of the spin selection rules the direction of the current is determine d by the helicity of the light and can be reversed by switching the helicit y from right to left handed. A microscopic model is presented which describ es the origin of the photon helicity driven current. The model suggests tha t the system behaves as a battery which generates a spin polarized current.