Whirling plasmons: Angular momentum selection rule

A study was conducted to demonstrate a plasmonic nanostructure that exhibited a crucial role of an angular momentum (AM) selection rule in a light-surface plasmon scattering process. The intrinsic AM of the incident radiation was coupled to the extrinsic momentum of the surface plasmons through spin-orbit interaction that was was manifested by a geometric Berry phase. This effect helped in achieving a symmetry breaking that resulted in a spin-dependent enhanced transmission through coaxial nanoapertures in rotationally symmetric structures. The coaxial nanoaperture was milled by a focused ion beam into a 200-nm-thick gold film evaporated onto a glass wafer. The inner and the outer radii of the ring slit were 250 and 350 nm, while the aperture was designed to be a single mode system.