Fundamental Limits in the Coupling between Light and 2D Polaritons

Polaritons in 2D materials have been extensively studied over the past decade due to their fundamental interest and as a platform for applications in telecommunications and sensing. The wavelength of these polaritons is... [ view full abstract ]

Polaritons in 2D materials have been extensively studied over the past decade due to their fundamental interest and as a platform for applications in telecommunications and sensing. The wavelength of these polaritons is generally small compared to that of a photon of the same frequency, and thus these excitations evolve in the electrostatic regime. This property makes them attractive to manipulate light at deep-subwavelength distances, although it simultaneously implies that their in/out-coupling to propagating light is intrinsically weak.

In this work, we address some fundamental limits in the coupling of radiation to 2D polaritons. We study the scattering properties of 0D and 1D scatterers over a 2D or finite-thickness layer and find a generalization of the optical theorem to 2D polaritons, which we express as a maximum possible value of their effective polarizability. Remarkably, this value is independent of material and we write the result as a universal curve that is applicable to any layer thickness in the electrostatic approximation. Additionally, this result leads to a maximum light-polariton coupling cross-section. We formulate our results for both 0D and 1D scatterers, including material edges, and present them in simple closed-form expressions.

This work has been supported in part by the Spanish MINECO (MAT2017-88492-R and SEV2015-0522) and the European Commission (Graphene Flagship 696656, Marie Skłodowska-Curie 713673). Eduardo Brioso Dias acknowledges support from a “la Caixa” INPhINIT Fellowship Grant.