Transient Infrared Catastrophes in Correlated Electron Fluids and the Puzzles of Photoemission Spectra in Alkali Metals



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We propose an explanation for the pronounced anomalous peak in the electronic density of states seen near the Fermi energy in angular-resolved photoemission experiments in alkali metals. We argue that a significant fraction of holes left behind the photo-ejected electron are not wavepacket-like objects characteristic of a Fermi liquid. Instead, this special type of holes are relatively localized objects that are better thought of as vacancies in an electronic solid. The peak near the Fermi energy corresponds, then, to an infrared divergence resulting from recoil currents of the electronic fluid. We consider additional non-adiabatic effects of photoexcitation being much faster than the electrons and plasmon modes. While these effects may also contribute to the said anomalous peak in the photoemission spectra, the contribution is likely insignificant.



Correlated electrons, Fermi liquid, Photoemission, ARPES, Alkali metals, Infrared catastrophe, Many-body interaction, Wigner crystal, Phase transitions