Optically injected spin currents in semiconductors

We show that quantum interference of one and two photon absorption from a t wo color field allows one to optically inject ballistic spin currents in un biased semiconductors. The spin currents can be generated with or without a n accompanying electrical current and can be controlled using the relative phase of the two colors. We characterize the injected spin currents using s ymmetry arguments and an eight-band Kane model.