Plasmonic modes at inclined edges of anisotropic 2D materials

Abstract

Confined modes at the edge arbitrarily inclined with respect to optical axes of nonmagnetic anisotropic 2D materials are considered. By developing the exact Wiener-Hopf and approximated Fetter methods we studied edge modes dispersions, field and charge density distributions. 2D layer is described by the Lorentz-type conductivities in one or both directions, that is realistic for natural anisotropic 2D materials and resonant hyperbolic metasurfaces. We demonstrate that, due to anisotropy, the edge mode exists only at wave vectors exceeding the nonzero threshold value if the edge is tilted with respect to the direction of the resonant conductivity. The dominating contribution to field and charge density spatial profiles is provided by evanescent 2D waves, which are confined both in space near the 2D layer and along the layer near its edge. The degree of field confinement along the layer is determined by wave vector or frequency mismatch between the edge mode and continuum of freely propagating 2D modes. Our analysis is suitable for various types of polaritons (plasmon-, phonon-, exciton-polaritons etc.) at large enough wave vectors. Thanks to superior field confinement in all directions perpendicular to the edge these modes look promising for modern plasmonics and sensorics.

Enabling propagation of anisotropic polaritons along forbidden directions via a topological transition

“…In turn, our results reveal two different regimes in which HPhPs propagate along mutually orthogonal directions, including the naturally forbidden [001] crystal direction for polaritonic propagation in bare -MoO 3 in the studied spectral range, and exotic intermediate states that unveil the topological origin of the transition, where HPhPs propagate within hyperbolas centered along both the [001] and [100] -MoO 3 directions. Our work opens up stimulating horizons for the investigation of topology-related features in polaritons in vdW materials, such as the existence of edge states (36) , topologically protected states, or the study of nodal points in momentum space protected by symmetries. In addition, extensive and effective control of the propagation of hyperbolic polaritons at the nanoscale is potentially possible via hybridization with plasmon polaritons (37) in various polaritonic heterostructures, thanks to the growing palette of polaritonic vdW materials that sum up to other conventional polaritonic media, such as SiC, aluminum nitride (AlN), or quartz.…”