Hermitian chiral boundary states in non-Hermitian topological insulators

TL;DR

This paper demonstrates that non-Hermitian topological insulators can host Hermitian chiral boundary states with real eigenenergies, which are robust and quantized, and introduces a topological Anderson insulator transition in such systems.

Contribution

It provides a method to construct Hermitian chiral boundary states from non-Hermitian topological insulators without parity-time symmetry, revealing new topological phases and transitions.

Findings

Hermitian chiral boundary states with real eigenenergies can exist in non-Hermitian systems.

These boundary states exhibit perfect, quantized transmission and robustness against disorder.

Non-Hermitian topological insulators can transition into topological Anderson insulators with finite disorder.

Abstract

Eigenenergies of a non-Hermitian system without parity-time symmetry are complex in general. Here, we show that the chiral boundary states of higher-dimensional (two-dimensional and three-dimensional) non-Hermitian topological insulators without parity-time symmetry can be Hermitian with real eigenenergies under certain conditions. Our approach allows one to construct Hermitian chiral edge and hinge states from non-Hermitian two-dimensional Chern insulators and three-dimensional second-order topological insulators, respectively. Such Hermitian chiral boundary channels have perfect transmission coefficients (quantized values) and are robust against disorders. Furthermore, a non-Hermitian topological insulator can undergo the topological Anderson insulator transition from a topological trivial non-Hermitian metal or insulator to a topological Anderson insulator with quantized transmission coefficients at finite disorders.