Tuneable Anisotropic Plasmonics with Shape-Symmetric Conducting Polymer Nanoantennas.

A wide range of nanophotonic applications rely on polarization-dependent plasmonic resonances, which usually requires metallic nanostructures that have anisotropic shape. Here, we demonstrate polarization-dependent plasmonic resonances by instead breaking symmetry via material permittivity. We show that molecular alignment of a conducting polymer can lead to a material with polarization-dependent plasma frequency and corresponding in-plane hyperbolic permittivity region. This result is not expected based only on anisotropic charge mobility but implies that also the effective mass of the charge carriers becomes anisotropic upon polymer alignment. We use this unique feature to demonstrate circularly symmetric nanoantennas that provide different plasmonic resonances parallel and perpendicular to the alignment direction. The nanoantennas are further tuneable via the redox state of the polymer. Importantly, polymer alignment could blue-shift the plasma wavelength and resonances by several hundreds of nanometers, forming a novel approach towards reaching the ultimate goal of redox-tunable conducting polymer nanoantennas for visible light. This article is protected by copyright. All rights reserved.