Abstract
The optical vortex beam has recently attracted significant attention because of carrying the orbital
angular momentum. We clarified that multipolar plasmons of metal nanodisks can be selectively excited
by circularly-polarized optical vortex beams. The orbital and spin angular momenta are transferred from
vortex photons to localized plasmons. Unfortunately, the mode volume of this plasmonic nanodisk
resonator is sub-micrometer dimension that is restricted by the diffraction limit of the surface plasmon
wave. In order to realize single-nanometer-sized cavities, we designed the tailored plasmonic structure
consisting of metal multimer surrounding a nanogap. This structure makes it possible to localize the
vortex field into the gap space with conserving the orbital and spin angular momenta. The transfer of
angular momenta from nano-vortex photons to molecules or nanoparticles causes rotational radiation
pressure, i. e., optical torque, which induces nano-vortex flow of molecules/particles and may lead to
chiral structuring of molecule/particle assemblies. We experimentally demonstrated rotational
manipulation of a polymer nano-bead using a gold nano-prism trimer structure.
