Phys. Rev. A 90, 043812 (2014)

Transformational plasmonics has recently emerged as a research topic to describe and exploit the coupling between surface electrons and incident light. However, an analogy with general relativity has also led research in another direction. Now, Muamer Kadic and co-workers from the Fresnel Institute in Marseille, France report using the plasmonic analogues of electromagnetic wormholes for controlling the propagation of surface plasmon polaritons. They focus on two different designs that fit the purpose: a toroidal cloak — a so-called handlebody that connects two holes on a metal surface — and the same toroidal cloak lying flat on a metal surface, resembling a doughnut. In both cases, full-wave numerical simulations show that surface plasmon polaritons propagate undisturbed in the metal, independent of the presence of an electromagnetic field in these metastructures. The computations, based on the finite element method, make the leap from the two- to the three-dimensional case, taking into account the plasmon polarization as well as the permittivity change at the interface between the different materials and air. Hoping to inspire experimental demonstrations of their results, the authors also infer the multi-layered versions of the proposed wormhole analogues for applications within the visible range. Simulations reveal unperturbated propagation of the wavefronts from a plasmon source in the middle for both the handlebody and doughnut cases. To create an actual device, you need homogeneous isotropic magnetic layers for the handlebody design and homogeneous isotropic dielectric layers for the doughnut design.