Tailoring optical responses of infrared plasmonic metamaterial absorbers by optical phonons.

Here we numerically and experimentally explore the rich phenomena in the optical responses and local electromagnetic fields of a MIM absorber mediated by the dispersive spacer. We first show that the line shape of the spectral absorption is strongly modified by the interaction between the plasmonic resonances and the optical phonons in the silicon dioxide spacer. Importantly, broadening the spectral absorption in the long wave infrared range is achieved by tuning the strength of coupling. Modification to the local electromagnetic field distribution in the epsilon-near-zero region is also numerically studied. The incident-angle dependence and polarization dependence of the broadened absorption spectrum are evaluated. We also show that the spectral broadening mechanism can be generalized to other frequency bands by employing different spacing materials such as silicon nitride and polydimethylsiloxane. Our results can be useful for designing spectrally selective thermal detectors and thermal emitters.