Topological network transport in on-chip phononic crystals

Rapid developments for topological materials have promoted the search for topological transport in the fields of condensed-matter physics and materials science. However, topological network transport, proposed in twisted bilayer graphene and soon after being explored in other two-dimensional materials, is still elusive despite extensive experimental efforts. Here, we implemented on-chip phononic crystal networks based on a network unit cell with six channels consisting of triangular prisms on a silicon substrate arranged in a honeycomb array. The topological network bulk transport in the gap of the bulk states of the original phononic crystal and the network edge transport in the gap of the network bulk states were visualized directly. These results offer a controllable platform for exploring topological transport in networks and may enable the realization of on-chip microultrasonic devices, such as splitters, filters, and signal processing in a monolithic elastic network.