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Injecting and controlling spin populations and currents in semiconductors using optically induced quantum interference effects

It is widely known that interband optical excitation of semiconductors such as GaAs using circularly polarized light can induced a net electron spin polarization because of the spin-orbit interaction which modifies the valence band states. In the last few years we have undertaken a series of theoretical and experimental investigations to explore how all-optical processes can be used to inject and control not only pure spin populations but also pure spin currents and pure charge currents or combinations of these. The various excitation schemes can be understood in terms of quantum interference of absorption pathways or, on a macroscopic level, nonlinear optical processes. The controlled currents and spin populations are typically generated by femtosecond laser pulses and detected via pump-probe techniques based on induced transmission changes or emitted THz radiation.