Exceptional points and spectral cusps from density-wave fluctuation

TL;DR

This paper identifies two types of singularities, exceptional points and spectral cusps, arising from density-wave fluctuations, which influence quasiparticle decay and Fermi arc formation, and are observable via ARPES techniques.

Contribution

It introduces the concept of exceptional points and spectral cusps as new singularities in density-wave fluctuation phenomena, with implications for spectral features and quasiparticle dynamics.

Findings

Exceptional points cause algebraic decay corrections in quasiparticle occupations.

Spectral cusps lead to Fermi arcs and threading structures in band spectra.

Both singularities are detectable through ARPES measurements.

Abstract

We report two types of singularities that arise from fluctuations during the formation of charge- or spin-density waves. The first is the exceptional point (EP), corresponding to a higher-order pole of the retarded Green's function. Such EPs lead to algebraic corrections in the decay of quasiparticle occupations and are observable through time-resolved angle-resolved photoemission spectroscopy (Tr-ARPES). The second is a spectral cusp, defined by the coalescence of three extrema in the real-frequency spectral function $A(\mathbf{k}, \omega)$. This cusp enforces the formation of Fermi arcs and induces a "threading" structure in the nearby band structure, both of which are directly observable in ARPES.