Exceptional points and spectral cusps from density-wave fluctuation

Zixi Fang; Chen Fang

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arXiv · 2511.21825

Exceptional points and spectral cusps from density-wave fluctuation

Zixi Fang·Chen Fang

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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 $A(\mathbf{k}, ω)$. 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.

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Zixi Fang, Chen Fang. 2025-11-26. Exceptional points and spectral cusps from density-wave fluctuation. https://arxiv.org/abs/2511.21825

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