Topological Plasmonic Chain with Retardation and Radiative Effects

We study a one-dimensional plasmonic system with nontrivial topology: a chain of metallic nanoparticles with alternating spacing, which in the limit of small particles is the plasmonic analogue to the Su-Schrieffer-Heeger model. Unlike prior studies we take into account long-range hopping with retardation and radiative damping, which is necessary for the scales commonly used in plasmonics experiments. This leads to a non-Hermitian Hamiltonian with frequency dependence that is notably not a perturbation of the quasistatic model. We show that the resulting band structures are significantly different, but that topological features such as quantized Zak phase and protected edge modes persist because the system has the same eigenmodes as a chirally symmetric system. We discover the existence of retardation-induced topological phase transitions, which are not predicted in the SSH model. We find parameters that lead to protected edge modes and confirm that they are highly robust under disorder, opening up the possibility of protected hotspots at topological interfaces that could have novel applications in nanophotonics.