New polaritonic materials in the THz range made of directionally solidified halide eutectics

Directionally solidified alkali halide binary eutectics have been recently proposed as THz polaritonic metamaterials based on their ordered microstructure and the suitable phonon–polariton resonances in the THz range of the spectrum. In the present work we focus on the search of new available eutectic systems both binary and ternary eutectics with well-ordered fibrous or lamellar microstructures and interparticle distances from 1 to several tens of microns. Simple effective homogenization models have been used to calculate effective permittivity and transmittance in the THz range of eutectic slices. This lets us identify the electromagnetic spectral ranges where hyperbolic dispersion is expected together with a significant transmittance value. The hyperbolic dispersion range shifts with microstructure size, that is, with growth parameters, showing that the materials response can be finely tuned by the manufacture conditions. Applications with these materials cover the electromagnetic range from 5 to 20 THz.