  Defects play a crucial role in the physical properties of crystals, whether
for classical or quantum systems. For example, in photonic/phononic crystals,
defects can serve as precise guidance and localization of classical
electromagnetic or mechanical waves. Rainbow concentrating, a recently proposed
exotic wave localization [Phys. Rev. Lett. 126, 113902 (2021)] exploits defects
to enable the collection and frequency routing of weak signals in real space.
In this paper, using a solid-state phononic crystal (PnC) plate, we
experimentally verify this phenomenon by deliberately infusing a homogeneous
graded dislocation, i.e., a line defect, into the PnC. Two PnCs separated by
the defect will breed deterministic interface states along with the defect,
offering rainbow trapping and concentrating for elastic waves. Our PnC-based
rainbow trappers and concentrators are scalable and configurable, promising for
advancing applications like energy harvesting, information processing, and
acoustofluidic manipulating.
