THz photonic bands of periodic stacks composed of resonant dielectric and nonlocal metal

The photonic band structures of superlattices composed of spatially-dispersive metal and polaritonic dielectric are theoretically investigated. The nonlocal relation between the electric current density and the electric field inside the metal layers is defined within the formalism of the Boltzmann kinetic equation, whereas the frequency dependent permittivity of the polar layers is modeled by a Lorentz-oscillator. Due to the large dielectric contrast between metal and polar components, the photonic band structure exhibits flat pass bands associated with Fabry-Perot resonances in the dielectric layers. There is also a wide stop band because of the existence of the polaritonic gap. We have compared our results with the predictions of the Drude-Lorentz model for the frequency-dependent metal permittivity. It is found that the nonlocal effect on the Fabry-Perot resonance bands is strong if their corresponding frequencies are within the interval where the difference between the impedances at both metal surfaces, predicted by the nonlocal and local formalisms, is maximal.