Spin-Momentum Locking in the Near Field of Metal Nanoparticles

Light carries both spin and momentum. Spin−orbit interactions of light come into play at the subwavelength scale of nano-optics and nanophotonics, where they determine the behavior of light. These phenomena, in which the spin affects and controls the spatial degrees of freedom of light, are attracting rapidly growing interest. Here we present results on the spin-momentum locking in the near field of metal nanostructures supporting localized surface resonances. These systems can confine light to very small dimensions below the diffraction limit, leading to a striking nearfield enhancement. In contrast to the propagating evanescent waves of surface plasmon-polariton modes, the electromagnetic near-field of localized surface resonances does not exhibit a definite positionindependent momentum or polarization. Close to the particle, the canonical momentum is almost tangential to the particle surface and rotates when moving along the surface. The direction of this rotation can be controlled by the spin of the incident light.