Effects of charges on the localized surface phonon polaritons in dielectric nanoparticles

Recently, there has been a great deal of interest in studying the surface phonon polariton (SPhP) modes in polar dielectrics due to their potential applications in the mid-infrared (MIR) spectral range. However, the effects of charges on the SPhP modes have not been discussed up to now. In fact, exotic electrons and electron-phonon (EPh) interactions widely exist in many nanostructures in practice. Here, we theoretically investigate effects of electrons and EPh interactions on the localized SPhPs in polar dielectric nanoparticles within the framework of Mie theory. Our results show that electrons have different effects on the localized SPhP modes in the nanostructures with different electron affinity. For particles with negative electron affinity, such as the MgO case, exotic electrons only lead to blueshifts of the SPhPs resonances with little effect on the magnitudes of resonance absorptions and electric near-field enhancements. While for particles with positive electron affinity, such as the Al₂O₃ case, except for blueshifts of the resonances, EPh interactions decrease the resonance absorptions largely, and almost annihilate multiple resonance modes into only one in multi-sphere nanostructures. Also, EPh terms reduce the electric near-fields dramatically to values far less than that of particles with no exotic electrons. Our results are helpful to the applications of polar dielectrics in nanoscale within the MIR spectral range.