Effects of Non-Hermiticity on Su-Schrieffer-Heeger Defect States

TL;DR

This paper investigates how non-Hermiticity affects defect states in the complex SSH model, revealing their emergence, disappearance, and symmetry-breaking transitions, with implications for topological and non-topological defect states.

Contribution

It provides a detailed analysis of defect state behavior in the non-Hermitian SSH model, including phase diagrams and symmetry-breaking phenomena, extending understanding beyond Hermitian topological systems.

Findings

Defect states can disappear into the continuum at high gain/loss.

Pairwise symmetry breaking leads to non-topological defect states.

Phase diagram maps defect state existence and symmetry-breaking regions.

Abstract

We study the emergence and disappearance of defect states in the complex Su-Schrieffer-Heeger (cSSH) model, a non-Hermitian one-dimensional lattice model containing gain and loss on alternating sites. Previous studies of this model have focused on the existence of a non-Hermitian defect state that is localized to the interface between two cSSH domains, and is continuable to the topologically protected defect state of the Hermitian Su-Schrieffer-Heeger (SSH) model. For large gain/loss magnitudes, we find that these defect states can disappear into the continuum, or undergo pairwise spontaneous breaking of a composite sublattice/time-reversal symmetry. The symmetry-breaking transition gives rise to a pair of defect states continuable to non-topologically-protected defect states of the SSH model. We discuss the phase diagram for the defect states, and its implications for non-Hermitian defect states.