Anomalous Non-Hermitian Topological Anderson Insulator

TL;DR

This paper uncovers symmetry-protected anomalous topological phases in strongly disordered non-Hermitian systems, revealing disorder-induced topological transitions and stable phases with quantized polarization.

Contribution

It demonstrates that engineered non-Hermitian disorder can induce and protect novel topological phases inaccessible to Hermitian systems, expanding the understanding of disorder and non-Hermiticity interplay.

Findings

Observation of a disorder-induced transition to a non-Hermitian topological Anderson insulator

Identification of a stable anomalous non-Hermitian TAI phase with quantized polarization

Zero-energy modes exhibit size-scaling (N/2)-mode coalescence within the anomalous phase

Abstract

Strong disorder drives conventional Hermitian systems into Anderson insulating states, suppressing all topological phases. Here, we unveil symmetry-protected, anomalous topological phases in the strong disorder limit of a non-Hermitian system, characterized by a scale-invariant merging of zero-energy modes. Using the maximally symmetric Jx lattice as an ideal platform and introducing specifically engineered (ABBA-type) symmetry-preserving non-Hermitian disorder, we observe a sequence of disorder-induced phase transitions: from a trivial insulator into and through a non-Hermitian topological Anderson insulator (TAI) phase, culminating in a stable anomalous non-Hermitian TAI phase characterized by a quantized polarization P_x \approx 0.25. Within this anomalous phase protected by the mobility gap, the zero-energy modes exhibit a distinct (N/2)-mode coalescence that scales with system size. Our findings demonstrate that non-Hermitian disorder engineered to preserve symmetry can induce and protect novel topological order inaccessible to conventional Hermitian disorder, thereby advancing the fundamental understanding of topological phenomena mediated by the interplay of disorder and non-Hermiticity.