Topological edge transport and one-way field localization in acoustic systems

Abstract

Recently, the fields of valley acoustics and nonreciprocal acoustics have become hotspots due to the potentials in developing various acoustic devices. In this presentation, we first introduce the concept of programmable routing of topological sound transport through boundary engineering, which reveals the inherent relation between the field symmetries of valley states and structural symmetries of sonic crystals. Three functional devices are exemplified, which are single-crystal-based topological delay-line filter, delay-line switcher and beam splitter. Our results clearly demonstrate the high-transmission valley transport along the folded boundaries, where reflection or scattering is prohibited at the sharp bending or corners due to topological protection. Then we show an analog of stimulated adiabatic passage in acoustic systems, where the cavities and time-varying couplings mimic discrete states and radiation pulses, respectively. With appropriate arrangements of coupling actions, acoustic waves can be efficiently transferred from the initial excited cavity to the target cavity in the forward direction, immune to the intermediate dark cavity. Whereas for the backward propagation, the acoustic energy is perfectly localized in the intermediate dark cavity and completely dissipated. We analytically, numerically, and experimentally demonstrate such unidirectional sound localization and unveil the essential role of zero-eigenvalue eigenstates in the adiabatic passage process.