Exceptional points in Fermi liquids with quadrupolar interactions

TL;DR

This paper demonstrates the presence of exceptional points, a type of non-Hermitian degeneracy, in the collective modes of Fermi liquids with quadrupolar interactions, revealing their topological nature and potential experimental signatures.

Contribution

It identifies and characterizes exceptional points in Fermi liquids with quadrupolar interactions, a novel finding in the study of collective modes.

Findings

Exceptional points occur in the collective mode spectrum.

Two stable modes coalesce at the exceptional point.

Topological properties of the singularity are explicitly shown.

Abstract

We show the existence of non-Hermitian degeneracies, known as exceptional points, in the collective mode spectrum of Fermi liquids with quadrupolar interactions. Through a careful analysis of the analytic properties of the dynamic quadrupolar susceptibility, we show that, in the weak attractive region, two stable collective modes coalesce to an exceptional point. We completely characterize this singularity, explicitly showing its topological properties. Experimental signatures are also discussed.