Realization of topological superlattices and the associated interface states in one-dimensional plasmonic crystals

In analogy to the Su-Schrieffer-Heeger (SSH) model, one-dimensional (1D) electromagnetic (EM) crystals can exhibit nontrivial topological properties. When a nontrivial EM crystal is in contact with its trivial counterpart, a topologically protected interface state is formed. While much attention has been focused on a single interface state, multiple interface states can interact collectively when suitable conditions are met, giving rise to nontrivial band topologies resembling the standard SSH model. Here, we study the topological properties of 1D metallic superlattices that support multiple interface states. We first demonstrate that a single interface state exists at the boundary between two topologically distinct metallic arrays that carry Bloch-like surface plasmon polaritons. Such an interface state is then used as the building block for further constructing the superlattices. By exploiting the separation between two dimerized interface states and the distinct inter- and intrainterface configurations to facilitate different intracell and intercell interactions, we vary the band topology of the superlattices. More importantly, a new superlattice interface state is formed when trivial and nontrivial superlattices are brought together. The superlattice interface state is found to have smaller angular divergence and longer localization length than its single counterpart, thus is desired for robust signal transmission and a high finesse cavity.