Symmetry-Protected Bipolar Skin Effect and its Topological Breakdown in Disordered Non-Hermitian Systems

TL;DR

This paper reveals a Z_2 topological bipolar skin effect in a non-Hermitian Rashba chain, showing its robustness against moderate disorder and its breakdown before Anderson localization, thus advancing understanding of disorder effects in non-Hermitian topological systems.

Contribution

The study introduces a Z_2 topological bipolar skin effect in a non-Hermitian Rashba chain and maps its stability under disorder, highlighting a hierarchical breakdown of topology.

Findings

Z_2 bipolar skin effect localizes spin states at opposite boundaries

The skin effect is robust against moderate disorder

It collapses before the onset of Anderson localization

Abstract

The interplay between non-Hermitian topology and disorder remains a central puzzle in open quantum systems. While the non-Hermitian skin effect (NHSE) is known to be robust against weak perturbations, its fate under strong disorder, particularly in the presence of spin-orbit coupling (SOC), is not fully understood. Here, we uncover a Z_2 topological bipolar skin effect in a non-Hermitian Rashba chain, where spin-up and spin-down eigenstates localize at opposite boundaries. By strictly computing the Lyapunov exponents and introducing a biorthogonal spin-separation index, we map the global phase diagram and reveal a hierarchical breakdown of topology. We demonstrate that the Z_2 skin effect is protected against moderate disorder but collapses into a trivial skin phase before the ultimate onset of Anderson localization. Our results establish a distinct regime of disorder-robust topological non-reciprocity, distinguishable from both the trivial bulk limit and the Anderson localized phase.