$\mathcal{PT}$-breaking threshold in spatially asymmetric Aubry-Andre Harper models: hidden symmetry and topological states

TL;DR

This paper investigates the $ ext{PT}$-breaking threshold in spatially asymmetric Aubry-Andre Harper models with gain and loss, revealing a hidden symmetry that ensures a finite threshold and the robustness of topological edge states.

Contribution

It uncovers a hidden symmetry enabling finite $ ext{PT}$-breaking thresholds in asymmetric models and demonstrates the resilience of topological states in the broken phase.

Findings

Finite $ ext{PT}$-breaking threshold depends on gain-loss location.

Hidden symmetry is crucial for the threshold's existence.

Topological edge states remain robust after $ ext{PT}$ symmetry breaking.

Abstract

Aubry-Andre Harper (AAH) lattice models, characterized by reflection-asymmetric, sinusoidally varying nearest-neighbor tunneling profile, are well-known for their topological properties. We consider the fate of such models in the presence of balanced gain and loss potentials $\pm i\gamma$ located at reflection-symmetric sites. We predict that these models have a finite $\mathcal{PT}$ breaking threshold only for {\it specific locations} of the gain-loss potential, and uncover a hidden symmetry that is instrumental to the finite threshold strength. We also show that the topological edge-states remain robust in the $\mathcal{PT}$-symmetry broken phase. Our predictions substantially broaden the possible realizations of a $\mathcal{PT}$-symmetric system.