Acoustic valley states and acoustic valley transport in sonic crystals

Abstract

We report the discovery of acoustic valley states in sonic crystals and the observation of the valley transport in the domain walls. The concept of valley pseudospin, labeling quantum states of energy extrema in momentum space, is attracting attention for its potential as a new type of information carrier. Inspired by the recent valley related phenomenon in election systems, the acoustic version of valley states in sonic crystals is studied and the vortex nature of such states is revealed. The extraordinary chirality of valley vortex states may provide new possibilities in sound manipulations and will be appealing to scalar acoustics since the absence of spin degree of freedom here. We further experimentally observe the topological valley transport of sound in sonic crystals. The acoustic valley transport is confined in the domain walls of the sonic crystals and behaves negligible reflection to the interface corners. The acoustic valley transport of sound, strikingly different from that in traditional sound waveguides, may serve as the basis for designing devices with unconventional functions.