Visualization of flexible large-area acoustic energy conveying enabled by valley-dependent Landau bulk modes

While conventional topological states can be used for robust acoustic energy transportation, the energy capacity is limited and the propagation route is also heavily constrained. In this work, we show that Landau levels in acoustic systems can offer exciting new avenues for transporting acoustic energies. In particular, we realize valley-dependent Landau levels in a two-dimensional inhomogeneous acoustic system induced by synthetic in-plane magnetic fields. The band diagrams of the 0th- and 1st-order Landau levels are experimentally measured and their robustness of propagation against defects is also experimentally validated. Promising ways for acoustic energy transportation enabled by the Landau levels, such as large-area transportation and snake-like transportation are experimentally demonstrated. Importantly, we achieve topological propagation along an arbitrary prescribed path using unique features of the valley-dependent Landau levels for the first time in experiment, which is a significant advancement beyond what can be achieved using conventional acoustic topological states based on valley/spin Hall physics. These remarkable features open up promising opportunities for developing novel acoustic devices to realize robust, broadband, and flexible large-area acoustic energy conveying.