Surface Exciton Polaritons and Near-Zero Permittivity Surface Waves Supported by Artificial Organic Hyperbolic Metamaterials

Abstract: Hyperbolic metamaterials enable extreme light confinement and control of photonic states, but their realization has been restricted to inorganic architectures. Here, a fully organic route to fabricate artificial hyperbolic metamaterials based on multilayered thin films of J-aggregate carbocyanine dyes alternated with polyelectrolytes is introduced. These structures exhibit strong optical anisotropy and experimentally support hyperbolic surface exciton polaritons and, for selected dyes, additional surface waves in near-zero permittivity regimes. Spectroscopic ellipsometry confirms a uniaxial dielectric tensor with negative in-plane and positive out-of-plane components, close to the absorption peaks of the constituent J-aggregates. This anisotropy is preserved across individual layers, demonstrating the robustness of the layer-by-layer approach and enabling the coupling of surface exciton polaritons and near-zero permittivity modes even in films only a few nanometres thick. Transfer-matrix simulations based on the obtained dielectric tensor reproduce the coupling conditions for all thicknesses, validating the optical model. Structural characterization reveals the link between optical anisotropy and supramolecular order, with preferential in-plane molecular orientation and the evolution from discrete nanostructures to continuous films as deposition progresses. These organic hyperbolic metamaterial architectures, associated with narrow excitonic resonances from J-aggregates, offer a unique platform for tailoring emission, energy transport, and exploring polariton dynamics at the nanoscale.