Edge states in non-Hermitian composite acoustic Su Schrieffer Heeger chains

Non-Hermiticity alone can trigger topological phase transition in physical systems. Here, we construct different unit cells in an acoustic Su Schrieffer Heeger chain with different distributions of onsite losses. We theoretically and numerically investigate the different edge modes that can occur at the domain walls of different finite chains. Three types of edge modes are identified. The first type comes from the topology of the unit cells. The second type comes from the local Parity symmetry at the interface, which are cavity modes. The third one comes from the Parity-Time symmetric domain wall. The robustness against coupling disorder is then examined, confirming the robustness of the topologically protected modes. The evolution with increasing disorder of the interface modes due to the Parity-Time symmetric domain wall is singular as they appear first as more robust than the cavity modes before diverging. These results show the ability of the onsite losses ingredient to control wavefields.