Exceptional rings in two-dimensional correlated systems with chiral symmetry

TL;DR

This paper explores how chiral symmetry in two-dimensional correlated systems leads to the formation of novel topological degeneracies called symmetry-protected exceptional rings (SPERs), revealed through theoretical models and dynamical mean-field theory.

Contribution

It introduces the concept of SPERs in chiral symmetric correlated systems and demonstrates their emergence using non-Hermitian Dirac Hamiltonians and dynamical mean-field theory.

Findings

SPERs are protected by symmetry in non-Hermitian systems.

SPERs persist beyond simple Dirac models, linked to a zero-th Chern number.

The study connects symmetry, non-Hermiticity, and topological degeneracies.

Abstract

Emergence of exceptional points in two dimensions is one of the remarkable phenomena in non-Hermitian systems. We here elucidate the impacts of symmetry on the non-Hermitian physics. Specifically, we analyze chiral symmetric correlated systems in equilibrium where the non-Hermitian phenomena are induced by the finite lifetime of quasi-particles. Intriguingly, our analysis reveals that the combination of symmetry and non-Hermiticity results in novel topological degeneracies of energy bands which we call symmetry-protected exceptional rings (SPERs). We observe the emergence of SPERs by analyzing a non-Hermitian Dirac Hamiltonian. Furthermore, by employing the dynamical mean-field theory, we demonstrate the emergence of SPERs in a correlated honeycomb lattice model whose single-particle spectrum is described by a non-Hermitian Dirac Hamiltonian. We uncover that the SPERs survive even beyond the non-Hermitian Dirac Hamiltonian, which is related to a zero-th Chern number.