Pure spin currents represent non-equilibrium distributions where free carriers, electrons or holes, with the spin “up” propagate mainly in one direction and equal number of carriers with the spin “down” propagates in the opposite direction. This state is characterized by zero charge current because electric currents contributed by spin-up and spin-down quasiparticles cancel each other, but leads to accumulation of the opposite spins at the opposite edges of the sample.

In the present talk we discuss a possibility to create pure spin currents in semiconductor structures by optical means. We show that pure spin currents can be optically injected in semiconductor quantum wells by linearly polarized or unpolarized light. The microscopic description of the effect is presented for (i) inter-band optical transitions in undoped quantum wells as well as for (ii) direct inter-subband and (iii) indirect intra-subband (Drude-like) transitions in n-doped structures.

Experimentally, pure spin currents can be observed by studying the spatial distribution of spin density in the quantum well plane. An alternative method is to convert the pure spin current into an electric current, e.g., by applying an external magnetic field which polarizes free carrier spins, and measure the electric response.

Page created on March 27, 2007.