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Non-Hermitian systems can exhibit a counterintuitive phenomenon where a single local boundary or disorder modifies the entire spectrum, no matter how large the system is. In such cases, all bulk modes become localized ``skin'' modes, and usual bulk topological invariants no longer correctly predict topological boundary modes. Generalizing Laughlin's gauge argument to complex fluxes, the authors derive a geometrical approach for the exact determination of the skin-mode spectrum. They also devise a new topological criterion for non-Hermitian particle-hole symmetric Hamiltonians based on complex analysis.
Lee et al. (Wed,) studied this question.