Acoustic flatbands in phononic crystal defect lattices.

In this paper, we investigate the acoustic flatbands (FBs) in phononic crystal (PnC) defect lattices. The defects are introduced into a PnC composed of periodic rigid rods in the air background. Since the acoustic energy is highly confined inside the PnC defects, the interaction between the defects can be described by the tight-binding model. We construct the PnC defects in two bipartite lattices, namely, the stub and Lieb lattices. The acoustic FBs can be observed for both of the lattices. Moreover, the acoustic FBs are protected by the chiral symmetry. That is, the FBs can be preserved even though the hopping strengths between the neighboring defects are perturbed. The proposed PnC defect lattices provide a feasible platform for the study of acoustic FB systems and topological insulators. [ABSTRACT FROM AUTHOR]