Local correlations necessitate waterfalls as a connection between quasiparticle band and developing Hubbard bands

TL;DR

This paper explains waterfalls in photoemission spectra as a natural consequence of the development of Hubbard bands from quasiparticle bands in correlated materials, aligning well with experimental observations in cuprates and nickelates.

Contribution

It demonstrates that waterfalls arise from local correlations during Hubbard band formation, providing a new understanding of spectral anomalies in strongly correlated systems.

Findings

Waterfalls are linked to Hubbard band development from quasiparticle bands.

Results from the Hubbard model match experimental spectra in cuprates and nickelates.

The study offers a natural explanation for high-energy spectral anomalies.

Abstract

Waterfalls are anomalies in the angle-resolved photoemission spectrum where the energy-momentum dispersion is almost vertical, and the spectrum strongly smeared out. These anomalies are observed at relatively high energies, among others, in superconducting cuprates and nickelates. The prevalent understanding is that they originate from the coupling to some boson, with spin fluctuations and phonons being the usual suspects. Here, we show that waterfalls occur naturally in the process where a Hubbard band develops and splits off from the quasiparticle band. Our results for the Hubbard model with $\textit{ab initio}$ determined parameters well agree with waterfalls in cuprates and nickelates, providing a natural explanation for these spectral anomalies observed in correlated materials.