Critical and noncritical non-Hermitian topological phase transitions in one-dimensional chains

In this work we investigate non-Hermitian topological phase transitions using real-space edge states as a paradigmatic tool. We focus on the simplest non-Hermitian variant of the Su-Schrieffer-Heeger model, including a parameter that denotes the degree of non-Hermiticity of the system. We study the behavior of the zero-energy edge states in the nontrivial topological phases with integer and semi-integer topological winding numbers, according to the distance to the critical point. We find that, depending on the parameters of the model, the edge states may penetrate into the bulk, as expected in Hermitian topological phase transitions. We also show that, using the topological characterization of the exceptional points, we can describe the intricate chiral behavior of the edge states across the whole phase diagram. Moreover, we characterize the criticality of the model by determining the correlation length critical exponent directly from numerical calculations of the penetration length of the zero-mode edge states.