Capturing Rainbow in On-Chip Phononic Crystals.

The control of elastic waves on a chip is essential for next-generation signal processing and integrated acoustics. In this Letter, we experimentally demonstrate an on-chip elastic-wave rainbow capture effect. A topological rainbow emerges by introducing pseudomagnetic field and pseudoelectric fields through structural modulation, where the elastic Landau level modes of different frequencies are spatially separated at distinct positions on the same chip. Interestingly, such bulk rainbow can be captured by the topological chiral edge states originated from the pseudo-magnetic field. We directly measure the rainbow distribution and the ensuing rainbow capture of elastic waves in a silicon-based phononic chip. Our Letter establishes a functional bridge between the bulk rainbow and topological edge states, offering new possibilities for designing the multifrequency devices of elastic waves.