Exceptional points in SSH-like models with a hopping amplitude gradient

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- P T -symmetric variation of the SSH model is introduced, in which the hopping amplitudes are nonreciprocal 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, to the best of our knowledge, tool for tailoring the spectrum of a non-Hermitian system.