Long lived surface plasmons on the interface of a metal and a photonic time-crystal

We predict the existence of surface plasmon polaritons at the interface between a metal and a periodically modulated dielectric medium, and find an unusual multi-branched dispersion curve of surface and bulk modes. The branches are separated by momentum gaps indicating intense amplification of modes, and display high and low group velocity ranging from zero to infinity at short wavelengths. We simulate how these SPP modes are formed by launching a properly engineered laser beam onto the metallic interface and examine their space-time evolution. The amplification of the surface plasmons at the interface of a photonic time-crystal offers a path to overcome plasmonic losses, which have been a major challenge in plasmonics.