Exceptional points in SSH-like models with hopping amplitude gradient

TL;DR

This paper investigates how a hopping amplitude gradient in a non-Hermitian SSH-like model influences the formation and properties of exceptional points, offering new ways to control spectral features for advanced applications.

Contribution

It introduces a non-Hermitian, non-PT-symmetric SSH model with a hopping gradient, revealing how this gradient affects exceptional points' number, position, and order.

Findings

Hopping amplitude gradient alters the number of EPs.

The position and order of EPs can be tuned by the gradient.

Nonreciprocal couplings are essential for EP existence.

Abstract

The Su-Schrieffer-Heeger (SSH) system is a popular model for exploring topological insulators and topological phases in one dimension. Recent interest in exceptional points has led to re-examination of non-Hermitian generalizations of many physical models, including the SSH model. In such non-Hermitian systems, singular points called exceptional points (EPs) appear that are of interest for applications in super-resolution sensing systems and topological lasers. Here, a non-Hermitian and non-PT-symmetric variation of the SSH model is introduced, in which the hopping amplitudes are non-reciprocal and vary monotonically along the chain. It is found that, while the existence of the EPs is due to the nonreciprocal couplings, the number, position, and order of the EPs can all be altered by the addition of the hopping amplitude gradient, adding a new tool for tailoring the spectrum of a non-Hermitian system.