Acoustic Weyl semimetals have attracted considerable attention owing to their topologically nontrivial band structures, characterized by Weyl points with nonzero topological charges and topologically protected Fermi-arc surface states. In conventional Weyl semimetals, chiral surface states are usually confined to the boundaries of a single material. However, topological interface states formed between two distinct Weyl semimetals, especially in chiral acoustic Weyl systems, remain largely unexplored. In addition, although antichiral edge states can be generated by modifying the flux configuration of the Haldane model, their acoustic realization through the stacking of Haldane-type structures with opposite chiralities has not yet been reported.
Here, we construct a three-dimensional acoustic Weyl semimetal based on a honeycomb lattice with chiral interlayer coupling. The chiral coupling induces an effective magnetic flux within the unit cell and effectively breaks time-reversal symmetry on fixed-k_z planes away from the Weyl-point planes. Each fixed-k_z subsystem can therefore be regarded as an acoustic analogue of a two-dimensional Haldane model, giving rise to topological bulk band gap characterized by nonzero Chern numbers. By reversing the winding direction of the chiral interlayer coupling, the topological charges of the Weyl points are inverted, and the Chern numbers of the k_z-resolved subsystems are correspondingly reversed. Exploiting this chirality-dependent topological property, we stack two acoustic Weyl semimetals with opposite chiralities to form a three-dimensional heterostructure supercell. For fixed-k_z planes away from the Weyl points, the zigzag interfaces support unidirectional topological interface states protected by a Chern-number difference of ±2, while the parallel outer surfaces host co-propagating antichiral surface states. The armchair interfaces also support similar unidirectional topological interface states.
Based on these findings, we further design a four-region heterostructure composed of acoustic Weyl semimetals with opposite chiralities. By exploiting the distinct propagation characteristics of antichiral surface states and topological interface states, directional acoustic wave splitting is realized through selective choice of the excitation position, as confirmed by numerical simulations of acoustic pressure-field distributions, transmission spectra, and wave-splitting ratios. The topological interface states exhibit backscattering-immune transport through 60° and 120° bends, demonstrating strong topological robustness. Furthermore, they remain stably confined along two separate propagation paths with multiple 90° turns, confirming strong spatial localization. This work demonstrates that acoustic Weyl semimetal heterostructures can support multiple topological transmission channels, providing a versatile platform for integrated and multifunctional topological acoustic devices.