  In analogous to the Su-Schrieffer-Heeger (SSH) model, one-dimensional (1D)
electromagnetic (EM) crystals can exhibit nontrivial topological properties. In
particular, 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 single interface state, multiple interface states
can interact collectively when under suitable conditions, giving rise to
trivial or nontrivial band topologies resembling to the standard SSH model.
Here, we study the topological properties of 1D metallic superlattices that
support multiple interface states. We first demonstrate single interface state
exists at the boundary between two topologically distinct metallic arrays that
carry Bloch-like surface plasmon polaritons. Such 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 intra-interface configurations to facilitate different intracell and
intercell interactions, we vary the band topology of the superlattices. More
importantly, 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 high
finesse cavity.
