Light-induced pure spin current*

We propose theoretically that a pure spin current without an accompanying charge current can be generated by light in magnetic tunneling junctions. The principle is based on a photovoltaic effect combined with the spin selectivity of the magentic electrodes of the junction. We demostrate this effect in graphene nanostructures by atomic first principles calculation. The results show that appreciable pure spin-currents and open circuit spin bias are generated in pure graphene nanostructures, and it can reach significant values if half metal with high spin polarization is used as the electrodes.