Exceptional Links and Twisted Fermi Ribbons in non-Hermitian Systems

TL;DR

This paper explores the emergence of exceptional links and Fermi ribbons in three-dimensional non-Hermitian systems, revealing new topological phenomena and potential applications in various physical platforms.

Contribution

It introduces the concept of exceptional rings and links in non-Hermitian 3D systems, along with Fermi ribbons as higher-dimensional Fermi arc analogues, advancing topological understanding.

Findings

Exceptional rings and links form in non-Hermitian 3D systems.

Fermi ribbons are open surfaces where the real part of the energy gap vanishes.

Potential applications in photonic crystals and metamaterials.

Abstract

The generic nature of band touching points in three-dimensional band structures is at heart of the rich phenomenology, topological stability and novel Fermi arc surface states associated with Weyl semimetals. Here we report on the corresponding scenario emerging in systems effectively described by non-Hermitian Hamiltonians. Remarkably, three-dimensional non-Hermitian systems have generic band touchings along one-dimensional closed contours forming exceptional rings and links in reciprocal space. The associated Seifert surfaces support open "Fermi ribbons" where the real part of the energy gap vanishes, providing a novel class of higher-dimensional bulk generalisations of Fermi arcs which are characterised by an integer twist number. These results have possible applications to a plethora of physical settings ranging from mechanical systems and optical metamaterials with loss and gain to heavy fermion materials with finite-lifetime quasiparticles. In particular, photonic crystals provide fertile ground for simulating the exuberant phenomenology of exceptional links and their concomitant Fermi ribbons.