Edge states in a non-Hermitian topological crystalline insulator

Breaking Hermiticity in topological systems gives rise to intriguing phenomena, such as the exceptional topology and the non-Hermitian skin effect. In this work, we study a non-Hermitian topological crystalline insulator sitting on the Kekule texture-modulated honeycomb lattice with balanced gain and loss. We find that the gaplessness of the topological edge states in the non-Hermitian system is insensitive to edge geometries under moderate strength of gain and loss, unlike the cases of Hermitian topological crystalline insulators that depend on edge geometries crucially. We focus on two types of gain and loss configurations, which are PT symmetric and PT asymmetric, respectively. For the PT-symmetric configuration, the Dirac point of the topological edge states in the Hermitian molecular-zigzag-terminated ribbons splits into a pair of exceptional points. The edge gap in the Hermitian armchair-terminated ribbons vanishes and a Dirac point forms as far as moderate gain and loss is induced. The band gaps of edge and bulk states in the Hermitian armchair-terminated ribbons close simultaneously for the PT-asymmetric configuration.

Automated summary

Breaking Hermiticity in topological systems leads to intriguing phenomena, such as exceptional topology and the non-Hermitian skin effect. This work focuses on a non-Hermitian topological crystalline insulator on a Kekule texture-modulated honeycomb lattice with balanced gain and loss. The study finds that the gaplessness of the topological edge states in the non-Hermitian system is insensitive to edge geometries under moderate strength of gain and loss.