Plasmon canalization and tunneling over anisotropic metasurfaces

Abstract

We discuss the possibility of plasmon canalization, collimation, and tunneling over ultrathin metasurfaces, enabled by extreme anisotropy in their complex conductivity dyadic. The interplay between anisotropy, conductivity-near-zero, and loss is exploited here to derive general conditions for plasmon canalization and efficient energy transport. We also demonstrate how the intrinsic in-plane anisotropy of black phosphorus can provide a natural platform to engineer these conditions, exhibiting important advantages over isotropic plasmonic materials. Our findings have implications for plasmonic sensors, planar hyperlenses and plasmon steering over a surface, and they highlight the potential of 2D materials beyond graphene.

The Optical Properties and Plasmonics of Anisotropic 2D Materials

“…Therefore, BP films are treated as a model system to host the anisotropic and hyperbolic 2D plasmons . Great theoretical and experimental efforts have been devoted to investigating the plasmons in this natural anisotropic material. Below, we discuss the theoretical studies on the plasmon dynamics of BP films and the experimental progress in detecting BP plasmons, as well as the potential applications of plasmons in anisotropic 2D materials.…”

“…The above analysis of hyperbolic plasmons is based on the local assumption ( q →0), where σ is a function of the only variable ω. However, in the thin film of BP, the wavelength of plasmon polaritons in the hyperbolic regime is extremely confined ( q ≫ k 0 ) (Figure e), leading to the case where the nonlocal effect should be considered . Correas‐Serrano et al analyzed the anisotropic optical conductivity of BP and took a nonzero wave vector into account .…”

“…By exploiting the natural conductivity anisotropy, anisotropic 2D materials can add additional design flexibility in engineering metasurfaces. Take the plasmon canalization devices as an example . Previous implementations of such devices have always been based on modulation or arranging strips of isotropic materials, such as graphene and silver, to engineer metamaterials with suboptimal σ‐near‐zero topologies, in which the loss and the transverse conductivity component are important hindrances.…”

“…However, in the thin film of BP, the wavelength of plasmon polaritons in the hyperbolic regime is extremely confined (q ≫ k 0 ) (Figure 6e), leading to the case where the nonlocal effect should be considered. [77,83,94,95] Correas-Serrano et al…”

“…In the past few years, tremendous attention has been given to graphene plasmons, with a remarkable manifestation of high tunability and low loss . Recently, a number of theoretical efforts have been devoted to studying the plasmonic properties of BP, where anisotropic plasmon dispersions occur due to its band anisotropy . Fascinatingly, the hyperbolic plasmon polaritons, whose iso‐frequency contour is a hyperbola, are predicted to naturally exist in BP films, which originate from the coupling between the intraband and interband optical conductivity .…”