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Anomalous Behavior Induced by a Single Impurity in Non-Hermitian Topological Systems with Nonreciprocal Coupling
Junjie Wang1, Zhenyan Wang1, Xie Ma2
1College of Mechanical Engineering, Ningbo University of Finance & Economics, Ningbo 315175, China.
Entropy (Basel, Switzerland)
|May 26, 2026
Summary
Coupling an impurity to a nonreciprocal Su-Schrieffer-Heeger (SSH) chain alters spectral properties and bulk state localization. This impurity coupling enables control over non-Hermitian topological systems and their skin effects.
Area of Science:
- Condensed Matter Physics
- Topological Materials
- Quantum Mechanics
Background:
- Non-Hermitian topological systems exhibit boundary-dependent spectra and eigenstates due to skin effects.
- The Su-Schrieffer-Heeger (SSH) model is a foundational one-dimensional topological system.
Purpose of the Study:
- Investigate how impurity coupling affects a nonreciprocal SSH chain.
- Explore the control of spectral structure, zero modes, and bulk state localization via impurity coupling.
Main Methods:
- Theoretical analysis of a system with an impurity coupled to a nonreciprocal SSH chain at two points.
- Examination of spectral properties and eigenstate localization under varying nonreciprocal coupling strengths.
Main Results:
- Nonreciprocal impurity-chain couplings significantly alter the spectral structure and zero mode parameter regime.
- Impurity couplings induce effective boundary conditions, influencing zero mode spatial distribution.
- Tuning nonreciprocity modifies bulk state localization, leading to distinct coexisting boundary states in the unidirectional coupling regime.
- Bulk states exhibit skin phase transitions from conventional to bipolar skin states.
Conclusions:
- Impurity coupling provides a feasible method for controlling non-Hermitian topological systems.
- The interplay between impurity coupling and nonreciprocity offers rich phenomena in topological physics.
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