  Although topological mechanical metamaterials have been extensively studied
from a theoretical perspective, their experimental characterization has been
lagging. To address this shortcoming, we present a systematic laser-assisted
experimental characterization of topological kagome lattices, aimed at
elucidating their in-plane phononic and topological characteristics. We
specifically explore the continuum elasticity limit, which is established when
the ideal hinges that appear in the theoretical models are replaced by
ligaments capable of supporting bending deformation, as observed for instance
in realistic physical lattices. We reveal how the zero-energy floppy edge modes
predicted for ideal configurations morph into finite-frequency phonon modes
that localize at the edges. By probing the lattices with carefully designed
excitation signals, we are able to extract and characterize all the features of
a complex low-frequency acoustic regime in which bulk modes and topological
edge modes overlap and entangle in response. The experiments provide
unequivocal evidence of the existence of strong asymmetric wave transport
regimes at finite frequencies.

Materials Science