Selectable trapping or rotation of micro-particles using a plasmonic Archimedes spiral

We demonstrate selectable trapping or rotation of dielectric micro-particles by optical near fields generated in a plasmonic Archimedes spiral. Depending on the handedness of circularly polarized excitation, plasmonic near fields can be engineered into either a super-focusing spot for particle trapping or a plasmonic vortex for particle rotation. The optical forces are numerically analyzed. Experimentally, selectable trapping or rotation of single microsphere and sphere cluster are both realized.