In this work, we describe a localization phenomena, the “topological defect coalescence,” occurring in a non-Hermitian chain with an arbitrary number of defect sites. Specifically, it refers to the localization and coalescence of multiple defect eigenstates at a single defect site closest to the localization edge of the bulk non-Hermitian skin modes. This phenomenon is distinct from the conventional topological defect states in Hermitian systems, where the defect states are separately localized at their respective defect sites. The requirement for the onset of topological defect coalescence is the presence of nonreciprocal coupling which renders the chain non-Hermitian, as well as imaginary on-site potentials at the defect nodes. This allows the defect state coalescence and distribution to be modulated by both the defect site distribution and their corresponding on-site potentials, paving the way for possible applications. Furthermore, this phenomenon is realizable in various synthetic and experimentally realizable platforms, such as topolectrical and photonic systems.

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• Skin effect
• Topological phases of matter
• 1-dimensional systems
• Non-Hermitian systems
• Tight-binding model