Plasma-phonon polaritons in superlattices of semimetal bismuth and polaritonic material

Abstract

The THz and infrared photonic dispersion relations of superlattices composed of polaritonic material and bismuth (Bi) layers are theoretically investigated. The semimetal Bi presents a far-infrared response described by a Drude-like formula with a large high-frequency background dielectric constant. We have considered three different polaritonic materials: NaBr, LiCl and LiH, such that the Bi plasma frequency lies above, in-between and below the characteristic frequencies of the polaritonic materials, respectively. Investigating the photonic band structure of each superlattice, we have found that when the Bi plasma frequency lies below the polaritonic gap, appears a photonic pass band of negative dispersion for TM modes just above the longitudinal-optical phonon frequency, attributed to the frequency dependence of the permittivity for the polaritonic material and the large high-frequency background dielectric constant for Bi, that can be relevant to the metamaterials community.