Surface polaritons on left-handed spheres

TL;DR

This paper analyzes surface polaritons on left-handed spheres using complex angular momentum techniques, classifying resonant modes, and describing their properties, including unique whispering gallery modes with potential applications in plasmonics and cavity QED.

Contribution

It provides a detailed classification and physical description of surface polaritons on left-handed spheres, including their dispersion, damping, and novel whispering gallery modes.

Findings

Long-lived resonant modes are linked to surface polaritons.

Identifies a polariton analogous to the plane interface case.

Discovers whispering gallery surface polaritons unique to left-handed materials.

Abstract

We consider the interaction of an electromagnetic field with a left-handed sphere, i.e., with a sphere fabricated from a left-handed material, in the framework of complex angular momentum techniques. We emphasize more particularly, from a semiclassical point of view, the resonant aspects of the problem linked to the existence of surface polaritons. We prove that the long-lived resonant modes can be classified into distinct families, each family being generated by one surface polariton propagating close to the sphere surface and we physically describe all the surface polaritons by providing, for each one, its dispersion relation and its damping. This can be achieved by noting that each surface polariton corresponds to a particular Regge pole of the electric part (TM) or the magnetic part (TE) of the $S$ matrix of the sphere. Moreover, for both polarizations, we find that there exists a particular surface polariton which corresponds, in the large radius limit, to that supported by the plane interface. There also exists, for both polarizations, an infinite family of surface polaritons of whispering gallery type having no analogs in the plane interface case and specific to left-handed materials. They present a "left-handed behavior" (phase and group velocities are opposite) as well as a very weak damping. They could be very useful in the context of plasmonics or cavity quantum electrodynamics.