Reconfigurable topological modes in acoustic non-Hermitian crystals

Recent explorations show that the non-Hermiticity, associated with loss and/or gain, can play a surprisingly significant role in topological insulators, where the topological states can only penetrate the bulk structure if the topological phase changes in the interior. In this work, by introducing non-Hermiticity into an acoustic quadrupole topological insulator, the authors show experimentally that the topological corner and edge states could be engineered at any desired positions without a topological phase transition, making the bulk sites useful.