Non-Hermitian perspective of the band structure in heavy-fermion systems

TL;DR

This paper explores the non-Hermitian properties of the band structure in heavy-fermion systems using a Kondo lattice model, revealing exceptional points, band touchings, and unique spectral features influenced by interactions.

Contribution

It introduces a non-Hermitian perspective to heavy-fermion systems, demonstrating the emergence of exceptional points and spectral phenomena due to electron correlations.

Findings

Identification of exceptional points in the spectral weight.

Observation of band touching similar to Fermi arcs.

Discovery of a Fermi loop without defective points in the paramagnetic phase.

Abstract

We analyze a two-dimensional Kondo lattice model with special emphasis on non-Hermitian properties of the single-particle spectrum, following a recent proposal by Kozii and Fu. Our analysis based on the dynamical mean-field theory elucidates that the single-particle spectral weight shows the exceptional points (EPs). Correspondingly, the spectral weight exhibits the band touching, resulting in a structure similar to the "Fermi arc". Furthermore, we find an intriguing phenomenon arising from the periodicity of the lattice. The EPs generated by two distinct Dirac points merge and change into a hybrid point which vanishes as the exchange interaction is increased. Accordingly, the paramagnetic phase in the low temperature region shows a significant difference from non-interacting fermions: the imaginary part of the self-energy yields the "Fermi loop" without any defective points.