# Chiral-symmetry protected exceptional torus in correlated nodal-line semi-metals

## TL;DR

This paper investigates how non-Hermitian physics with chiral symmetry in a correlated nodal-line semi-metal leads to the formation of a symmetry-protected exceptional torus, affecting magnetic responses.

## Contribution

It introduces the concept of a symmetry-protected exceptional torus in a correlated semi-metal and analyzes its effects using dynamical mean-field theory and non-Hermitian physics.

## Key findings

- Nodal line transforms into a symmetry-protected exceptional torus.
- SPETs enhance magnetic susceptibility at weakly correlated sites.
- Non-Hermitian degeneracies influence external field responses.

## Abstract

We analyze a diamond-lattice Hubbard model with the spatially modulated Hubbard interaction. Our dynamical mean-field analysis with special emphasis on non-Hermitian properties elucidates that the gapless nodal line changes into symmetry-protected exceptional torus (SPET) at the Fermi level enclosing the three-dimensional open Fermi surface, which is unique to non-Hermitian physics with chiral symmetry. Furthermore, we also elucidate the effects of the SPETs on the magnetic response; our results based on the random-phase approximation combined with the the dynamical mean-field theory shows that SPETs enhance the magnetic susceptibility at the weakly correlated sites, exemplifying effects of non-Hermitian degeneracies on responses to external fields.