Emergent localized states at the interface of a twofold PT-symmetric lattice

Abstract

We consider the role of nontriviality resulting from a non-Hermitian Hamiltonian without band topology that conserves twofold PT symmetry assembled by interconnections between a PT-symmetric lattice and its time-reversal partner. Twofold PT symmetry in the lattice produces additional surface exceptional points that play the role of new critical points, along with the bulk exceptional point. We show that there are two distinct regimes possessing symmetry-protected localized states of which localization lengths are robust against non-Hermiticity parameter. The states are demonstrated by numerical calculation of a quasi-one-dimensional ladder lattice and a two-dimensional bilayered square lattice.