Non-Hermitian flatband generator in one dimension

TL;DR

This paper presents a systematic method for constructing non-Hermitian flatbands in one-dimensional two-band tight-binding models, revealing more flatband types than in Hermitian systems and including non-symmetry protected cases.

Contribution

It extends existing methods to generate flatbands to non-Hermitian systems, allowing for more diverse flatband types without symmetry constraints.

Findings

Non-Hermitian flatbands can be systematically constructed.

More types of flatbands are possible in non-Hermitian systems.

Non-symmetry protected flatbands exist in non-Hermitian models.

Abstract

Dispersionless bands -- flatbands -- have been actively studied thanks to their interesting properties and sensitivity to perturbations, which makes them natural candidates for exotic states. In parallel non-Hermitian systems have attracted much attention in the recent years as a simplified description of open system with gain or loss motivated by potential applications. In particular, non-Hermitian system with dispersionless energy bands in their spectrum have been studied theoretically and experimentally. Flatbands require in general fine-tuning of Hamiltonian or protection by a symmetry. A number of methods was introduced to construct non-Hermitian flatbands relying either on a presence of a symmetry, or specific frustrated geometries, often inspired by Hermitian models. We discuss a systematic method of construction of non-Hermitian flatbands using 1D two band tight-binding networks as an example, extending the methods used to construct systematically Hermitian flatbands. We show that the non-Hermitian case admits fine-tuned, non-symmetry protected flatbands and provides more types of flatbands than the Hermitian case.