Physical review. B./Physical review. B

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

Symmetry-protected exceptional rings in two-dimensional correlated systems with chiral symmetry