  Optical control of electronic spins is the basis for ultrafast spintronics:
circularly polarized light in combination with spin-orbit coupling of the
electronic states allows for spin manipulation in condensed matter. However,
the conventional approach is limited to spin orientation along one particular
orientation that is dictated by the direction of photon propagation. Plasmonics
opens new capabilities, allowing one to tailor the light polarization at the
nanoscale. Here, we demonstrate ultrafast optical excitation of electron spin
on femtosecond time scales via plasmon to exciton spin conversion. By
time-resolving the THz spin dynamics in a hybrid (Cd,Mn)Te quantum well
structure covered with a metallic grating, we unambiguously determine the
orientation of the photoexcited electron spins which is locked to the
propagation direction of surface plasmon-polaritons. Using the spin of the
incident photons as additional degree of freedom, one can orient the
photoexcited electron spin at will in a two-dimensional plane.
