Acoustic topological Jackiw-Rebbi states at symmetry broken interfaces.

Topological insulators, a fundamental concept in modern condensed matter physics, support localized states at the interfaces between insulators exhibiting different topological phases, which conventionally rely on explicit symmetry breaking. Here, we propose a mechanism to induce a real-space topological phase transition by spontaneous symmetry breaking, thereby establishing a weakly-coupled non-Hermitian double-well potential to generate a nontrivial Jackiw-Rebbi state. This state arises from intrinsic perturbations that trigger exceptional points at the interface, exhibiting unique robustness ensured by band degeneracy in complex band structure. By constructing an acoustic topological metagrating, we observe the Jackiw-Rebbi state with a constant phase jump that propagates along the metagrating surface, distinct from conventional localized topological modes, and experimentally demonstrate high-directivity topological radiation with an intensity enhancement of 20 dB and a divergence angle of 0.1 rad. Our findings open avenues for delocalized wavefront manipulation via the interplay between topology and symmetry, paving the way for engineering new acoustic topological devices for applications in filtering, sensing, and energy harvesting.