Electrodynamics of superlattices with ultra-thin metal layers: quantum Landau damping and band gaps with nonzero density of states

Abstract

© 2019 Optical Society of America. The transmission and absorption spectra of a periodic array of ultra-thin metal layers are calculated in the regime when size quantization of electron motion and their nonlocal contribution to conductivity play an essential role. In the THz region and in helium temperatures, this regime is realized if the thickness of metal layers is comparable to the skin-depth and metal film becomes partially transparent. Due to size quantization, the Landau damping is also quantized, leading to new resonances in surface impedances of metal film. An avoided crossing of these resonances with Fabry-Perot photonic pass bands gives rise to narrow band gaps where, nevertheless, the density of photonic states does not vanish. Such dark photonic states populating the new band gaps exhibit strongly anomalous dispersion and strong decay, as it is required by the Kramers-Kronig relations. The decay is due to the quantized Landau damping and it remains finite even in the collisionless limit.