The evolution of interface phonon–polariton modes in a finite superlattice with a structural defect
Using a transfer matrix method, we derive the dispersion equation for interface phonon–polariton modes (IPPMs) in a finite superlattice (SL) with a structural defect. The numerical results show that, in the nonradiative regime, there exist localized IPPMs (including retardation) inside or outside the Reststrahlen regions defined by the interval [ωTO, ωLO]. The localized IPPMs lie either in the minigaps or below and above the bulk bands, and their transversal electric field amplitudes are located in the vicinity of the defect layer or surface layers. The evolution of the IPPMs localized in the vicinity of a different interface can clearly be tracked. In addition, a brief analysis that radiative IPPMs evolve into nonradiative IPPMs is given.