Acoustic Valley Filter, Valve, and Diverter

The discovery of valley degrees of freedom in electronic and classical waves opened the field of valleytronics and offered the prospect for new devices based on valleys. However, the implementation of valley-based devices remains challenging in practice. Here, by taking advantage of the flexibility of phononic crystals in design and fabrication, the realizations of valley devices, or filters, valves, and diverters for acoustic waves are reported. All the devices are configured as the structures of input and output ports bridged by channels. The phononic crystals serving as ports allow the propagation of both valley polarizations, whereas the phononic crystals serving as channels, as they are narrow, only allow the propagation of single polarizations. For valley filters that achieve valley-polarized currents, the bridge channel is simply a straight single phononic crystal, but for valley valves that can turn off the valley-polarized currents, the channel consists of two parts, allowing the propagation of opposite valley polarizations. The valley diverters have one input port, and two output ports, and thus a branched channel, and the three parts in the channel allow the propagation of the same valley polarizations, so that the energy flow can be partitioned. The results may serve as a basis for developing advanced acoustic valley devices.