  Spintronics, which aims at exploiting the spin degree of freedom of carriers
inside electronic devices, has a huge potential for quantum computation and
dissipationless interconnects. Ideally, spin currents in spintronic devices
should be powered by a spin voltage generator able to drive spins out of
equilibrium and produce two spatially well-separated populations with opposite
spin orientation. Such a generator should work at room temperature, be highly
integrable with existing semiconductor technology, and work with neither
ferromagnetic materials nor externally applied magnetic fields. We have matched
these requirements by realizing the spintronic equivalent of a photovoltaic
cell. While the latter spatially separates photoexcited electron and hole
charges, our device exploits circularly polarized light to produce two
spatially well-defined electron populations with opposite spin. This is
achieved by modulating the phase and amplitude of the light wavefronts entering
a semiconductor (germanium) with a patterned metal overlayer (platinum). This
allows creating a light diffraction pattern with spatially-modulated chirality
inside the semiconductor, which locally excites spin-polarized electrons thanks
to electric dipole selection rules.
