抄録
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.
