Formation of Hubbard-like bands as a fingerprint of strong electron-electron interactions in FeSe

TL;DR

This study uses ARPES to reveal Hubbard-like bands in FeSe, demonstrating that strong local Coulomb interactions are crucial for understanding its electronic structure and related iron-based superconductors.

Contribution

The paper provides experimental evidence of Hubbard-like bands in FeSe and links these features to strong local electron-electron correlations using dynamical mean-field theory.

Findings

Hubbard-like bands observed at high binding energies in FeSe

Strong local Coulomb interactions are essential for accurate electronic structure modeling

Correlation effects influence the entire energy spectrum of FeSe

Abstract

We use angle-resolved photo-emission spectroscopy (ARPES) to explore the electronic structure of single crystals of FeSe over a wide range of binding energies and study the effects of strong electron-electron correlations. We provide evidence for the existence of "Hubbard-like bands" at high binding energies consisting of incoherent many-body excitations originating from Fe $3d$ states in addition to the renormalized quasiparticle bands near the Fermi level. Many high energy features of the observed ARPES data can be accounted for when incorporating effects of strong local Coulomb interactions in calculations of the spectral function via dynamical mean-field theory, including the formation of a Hubbard-like band. This shows that over the energy scale of several eV, local correlations arising from the on-site Coulomb repulsion and Hund's coupling are essential for a proper understanding of the electronic structure of FeSe and other related iron based superconductors.