Surface plasmonic Cherenkov radiation and symmetry breaking within a coherent nonlinear nanostructure

Abstract

Nonlinear conversions within the plasmonic structures are important for ultrafast nanophotonics; however, the impact of higher-order dispersion on nonlinear polaritonic efficiency remains unexplored. In this work, we uncover the role of higher-order dispersion and self-steepening on nonlinear surface-plasmon polaritons (NSPPs) within a coherent plasmonic interface that comprises an atomic medium doped on top of a low-loss negative-index metamaterial (NIMM) layer. This dispersion in the atomic medium--NIMM interface yields nonlinear plasmonic phase match and resonant launching of Cherenkov SPPs. We establish time-reversal and $\mathcal{PT}$ symmetry breaking for propagated NSPPs that yield asymmetric plasmonic comb excitation and anomalous plasmonic phase singularities. Our work thereby suggests a fingerprint for nonlinear plasmonic field evolution through the appearance of a Cherenkov field and develops a framework for designing a frequency selector and nanoscopic pulse shaper, which opens prospects for nonlinear nanophotonic applications.