Signatures of Topological Phonons in Superisostatic Lattices.

Soft topological surface phonons in idealized ball-and-spring lattices with coordination number z=2d in d dimensions become finite-frequency surface phonons in physically realizable superisostatic lattices with z>2d. We study these finite-frequency modes in model lattices with added next-nearest-neighbor springs or bending forces at nodes with an eye to signatures of the topological surface modes that are retained in the physical lattices. Our results apply to metamaterial lattices, prepared with modern printing techniques, that closely approach isostaticity.