Topological exceptional surfaces in non-Hermitian systems with parity-time and parity-particle-hole symmetries

TL;DR

This paper explores topological exceptional surfaces in non-Hermitian systems with $PT$ and $CP$ symmetries, revealing their stability and realization in lattice models of semimetals and superconductors.

Contribution

It demonstrates the existence and stability of $(d-1)$-dimensional exceptional surfaces in non-Hermitian systems with specific symmetries, a novel topological feature.

Findings

Exceptional surfaces can appear from band touching in $PT$ or $CP$ symmetric systems.

Topological stability of these surfaces is established.

Lattice models of semimetals and superconductors exhibit these degeneracies.

Abstract

We study a topological band degeneracy in non-Hermitian systems with parity-time ($PT$) and parity-particle-hole ($CP$) symmetries. In $d$-dimensional non-Hermitian systems, it is shown that $(d-1)$-dimensional exceptional surfaces can appear from band touching thanks to $PT$ or $CP$ symmetry. We investigate the topological stability and zero-gap quasiparticles for the exceptional surfaces due to the band degeneracy. We also demonstrate the band degeneracy by using lattice models of a topological semimetal and a superconductor.