Effect of Charge-neutrality Breaking on Localized Terahertz Waves in a Plate of Layered Superconductor

We study analytically the effect of charge-neutrality breaking on the spectrum of localized Josephson plasma waves (JPWs) in a plate of layered superconductor of finite thickness for the case of layers parallel to the interface. This effect results in the appearance of additional eigenmodes with anomalous dispersion and an additional forbidden region in the spectrum of localized modes near the Josephson plasma frequency. We consider both the surface and waveguide eigenmodes with symmetric and anti-symmetric field distribution with respect to the middle plane of the superconducting plate.