Spectral gaps in the near-field heat flux

We present a theoretical study of the modification of the near-field radiative heat transfer due to surface phonon-surface plasmon polariton coupling in bilayer systems made of a doped semiconductor and a polar dielectric. By tuning the surface-plasmon mode of the former material in resonance with the surface phonon modes of the latter one, the near-field spectral radiative heat flux can be suppressed in a frequency band gap. We show how mode hybridization is responsible for the opening of this spectral gap. By changing the carrier concentration we detune the surface plasmon-polariton from the surface phonon polariton. In this case, the band gap does not open. Furthermore, we show that the surface plasmon polariton of the top-most layer allows optimizing the total heat transfer between the bilayer structure as a function of the separation between them.