Creating compact localized modes for robust sound transport via singular flat band engineering

Abstract: We experimentally demonstrate the emergence of flat-band-induced compact-localized modes in acoustic Kagome lattices. Compact localized states populate singular dispersion bands characterized by band crossing, where a quadratic and a flat-band dispersion coalesce into a singularity. These conditions enable intriguing wave phenomena when the Hilbert Schmidt quantum distance, measuring the strength of the singularity, is nonzero. We report numerically and experimentally the formation of compact localized states (CLS), extremely localized in space and protected by dispersion flatness. In our system of coupled acoustic waveguides, sound waves are confined to propagate within tightly localized sites positioned both at the boundaries and within the interior of the lattice, achieving broadband and sustained confinement over time. This framework opens new avenues for the manipulation and transport of information through sound waves, with potential application in mechanics and acoustics, including communication, signal processing, and sound isolation. This work also expands the exploration of flat-band lattice physics within the realm of acoustics.