We demonstrate experimental focusing of surface plasmon polaritons beyond the plasmon diffraction limit using a super-oscillatory plasmonic antenna at the wavelength of 785nm, achieving a hot-spot as small as 300nm.

Plasmonic resonances are observed in metamaterials made of a topological insulator, Bi1.5Sb0.5Te1.8Se1.2, at the UV and visible frequencies due to the material’s interband transition and nontrivial surface conducting state.