Observation of topological edge states induced solely by non-Hermiticity in an acoustic crystal

Most existing non-Hermitian topological systems derive their nontrivial topology from Hermitian factors. Here, the authors report on the experimental observation of acoustic topological edge states induced solely by non-Hermiticity. They show that non-Hermiticity is able to create a topological band gap from a gapless Hermitian system. The study offers the possibilities for actively steerable topological wave manipulations in applications ranging from acoustics to photonics.