Probing Fermi liquid exceptional points through AC conductivity

Abstract

Exceptional points, which are topological non-Hermitian degeneracies, show up in the collective mode spectrum of Fermi Liquids with high angular momentum interactions. In this paper, we look for signatures of these non-trivial singularities by computing the AC conductivity of Fermi liquids with dipolar and quadrupolar interactions in a narrow slab. We show that the finite size of the slab imprints clear signatures of the structures of the collective mode spectrum in the conductivity as well as in the dephasing between the electric field and the current density in a wide range of coupling constants. In particular, we show the fingerprints of exceptional points, observed in the weak attractive dipolar and/or quadrupolar regime. The main result does not depend on the specific model of quasi-particle interactions. We also discuss some actual compounds where these phenomena could be experimentally observed.