Valley-projected edge modes observed in underwater sonic crystals

Here, we report an experimental study on the valley-projected edge states for underwater sound, which propagates along the interface separating two topologically distinct acoustic valley Hall insulators. The topological edge states are directly observed in our ultrasound scanning experiments, together with a solid evidence for the valley-selective excitation. Furthermore, we demonstrate an intriguing sound splitter built by topologically different acoustic valley Hall insulators. All experimental data agree well with our numerical results. Prospective applications can be anticipated, such as for underwater sound signal processing and ocean noise control.