  Surface plasmons, free-electron collective oscillations in metallic
nanostructures, provide abundant routes to manipulate light-electron
interactions that can localize light energy and alter electromagnetic field
distributions at subwavelength scales. The research field of plasmonics thus
integrates nano-photonics with electronics. In contrast, electronics is also
entering a new era of spintronics, where spin currents play a central role in
driving devices. However, plasmonics and spin-current physics have so far been
developed independently. Here, we demonstrate the generation of spin currents
by surface plasmons. Using Au nanoparticles embedded in a Pt/BiY2Fe5O12 bilayer
film, we show that, when the Au nanoparticles fulfill the
surface-plasmon-resonance condition, spin currents are generated across the
Pt/BiY2Fe5O12 interface. This plasmonic spin pumping results from
nonequilibrium states of spins excited by surface-plasmon-induced evanescent
electromagnetic fields in the BiY2Fe5O12 layer. Such plasmonic spin pumping
will invigorate research on spin-current physics, and pave the way for future
spin-based plasmonic devices.
