Selective excitation of multipolar spoof plasmons using orbital angular momentum of light

TL;DR

This paper demonstrates that orbital angular momentum of light can selectively excite multipolar spoof plasmons in solids, revealing new light-matter interaction mechanisms beyond electric dipole transitions.

Contribution

It provides the first visual evidence of dipole-forbidden multipolar excitations in solids induced by vortex beams, confirming angular momentum transfer in a solid-state system.

Findings

Selective excitation of multipolar spoof plasmons by vortex beams

Confirmation of angular momentum conservation in solid-state excitations

Visualization of dipole-forbidden multipolar excitations in a solid

Abstract

The nature of light-matter interaction is governed by the spatial-temporal structures of a light field and material wavefunctions. The emergence of the light beam with transverse phase vortex, or equivalently orbital angular momentum (OAM) has been providing intriguing possibilities to induce unconventional optical transitions beyond the framework of the electric dipole interaction. The uniqueness stems from the OAM transfer from light to material, as demonstrated using the bound electron of a single trapped ion. However, many aspects of the vortex light-matter interaction are still unexplored especially in solids with extended electronic states. Here, we unambiguously visualized dipole-forbidden multipolar excitations in a solid-state electron system; spoof localized surface plasmon, selectively induced by the terahertz vortex beam. The results obey the selection rules governed by the conservation of the total angular momentum, which is numerically confirmed by the electromagnetic field analysis. Our results show light's OAM can be efficiently transferred to an elementary excitation in solids.