Correlation effects on non-Hermitian point-gap topology in zero dimension: reduction of topological classification

TL;DR

This paper investigates how electron correlations influence non-Hermitian topological phases in a zero-dimensional system, revealing that correlations can eliminate certain exceptional points and connect different topological phases without gap closure.

Contribution

It demonstrates that correlations can reduce the topological classification in non-Hermitian systems, analogous to Hermitian cases, and introduces the concept of a Mott exceptional point involving spin degrees of freedom.

Findings

Correlations destroy an exceptional point at the topological transition.

Correlations enable continuous connection between topological phases without gap closing.

Discovery of a Mott exceptional point involving only spin degrees of freedom.

Abstract

We analyze a zero-dimensional correlated system with special emphasis on the non-Hermitian point-gap topology protected by chiral symmetry. Our analysis elucidates that correlations destroy an exceptional point on a topological transition point which separates two topological phases in the non-interacting case; one of them is characterized by the zero-th Chern number $N_{0\mathrm{Ch}}=0$, and the other is characterized by $N_{0\mathrm{Ch}}=2$. This fact implies that correlations allow to continuously connect the two distinct topological phases in the non-interacting case without closing the point-gap, which is analogous to the reduction of topological classifications by correlations in Hermitian systems. Furthermore, we also discover a Mott exceptional point, an exceptional point where only spin degrees of freedom are involved.