Anderson localized transport in non-Hermitian spoof surface plasmon polariton structures

Anderson localization, a fundamental wave phenomenon, is a challenging problem in quasiparticle transport, exacerbated in the presence of dissipation. Of late, however, a few demonstrations of Anderson localization in non-Hermitian structures have been made. In the domain of electromagnetics of structured materials, spoof surface plasmon polaritons are a very interesting concept where structured metallic surfaces sustain bound states even at very low frequencies. The metallic non-Hermiticity, in an environment of possible disorder, makes this system an interesting case-study for mesoscopic transport, although the idea of disordered structures for spoof plasmons is not commonly encountered in literature. Here, we present experimental evidence of Anderson localization in hybrid polariton-photon states within a disordered, non-Hermitian environment. Disorder is introduced by perturbing the periodic microstructure while maintaining surface confinement. Localization enhances the plasmonic intensity by about a factor of three as compared to the conventional periodic structure. We experimentally characterize the intensity distribution, dispersion properties, and generalized conductance within the Anderson localized regime. A significant decrease in both localization length and its fluctuations is observed with increasing disorder strength. The inverse participation ratio shows the anticipated linear dependency on localization length. Our results offer experimental proof of Anderson localization in hybrid polariton-photon states, showcasing the influence of disorder in boosting plasmonic intensity. This elucidates potential applications in fields requiring controlled wave transport in disordered settings.