Excitonic Optical Tamm States: a first step for a fully-plastic era in the photonic technology: New Horizons in Nanophotonics, Theo Murphy Meeting, The Royal Society, UK

Decades ago, molecular crystals shown metallic reflection associated with strong interactions between neighboring molecular excitons. [1] In these organic materials the individual molecules are spatially distributed in the crystal lattice and can be considered as small local dipoles that can be excited collectively under specific conditions. This behavior is responsible for the optical properties of the material, whose real part of the permittivity can achieve negative values resembling metallic behavior in a restricted wavelength range. Interestingly, whilst metals support Surface Plasmon-Polaritons, a molecular crystal can support Surface Exciton-Polaritons. [2] Recently, we showed that it is possible to obtain metal-like properties in heavily dye-doped polymers, where the polar molecules (J-aggregates) are randomly spatially distributed. [3] The optical properties of these dye-doped polymers can reach negative values on the real part of the permittivity giving a metallic appearance to the organic material.
Tamm Optical States are lossless interface modes propagating along the surface between two highly reflective periodic dielectric structures. [4] Among their most interesting properties is the possibility to excite them within the light cone. One of these periodic structures can be replaced by a metal with a high reflectance value in region of the photonic stopband of the other periodic structure; these modes are known as Tamm-Plasmon States and are characterized by parabolic dispersion relations. Unfortunately metals are a not tunable materials, their properties are established at the atomic scale, limiting the possibilities of modal design. Recently we have demonstrated that special Tamm Optical States (Excitonic Optical Tamm States) with tunable dispersion curves can be excited at the interface between a Distributed Bragg Reflector (DBR) and a metal-like organic thin film. [5] The dispersion curves of these novel modes show two cut-off wavelengths controlled by the mismatch of the mode propagation and the high reflectance bandwidth. These results reveal the potential applications of materials doped with strongly interacting excitons in photonic structures where metals could be replaced by organic polymers.

REFERENCES
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[4] A. Kavokin et al., Phys. Rev. B 72, 233102 (2005).
[5] S. Núñez-Sánchez, M. Lopez-Garcia, et al. , ACS Photonics 2016, DOI:acsphotonics.6b00060.