Direct observation of dispersive lower Hubbard band in iron-based superconductor FeSe

TL;DR

This study combines ARPES and DMFT to reveal a dispersive lower Hubbard band in FeSe, demonstrating strong electronic correlations and intermediate coupling strength crucial for understanding iron-based superconductors.

Contribution

The paper provides the first direct observation of a dispersive lower Hubbard band in FeSe, linking experimental ARPES data with theoretical DMFT calculations.

Findings

Dispersive lower Hubbard band observed in FeSe

Strong deviations from single-electron approximation in the spectrum

Evidence of intermediate coupling strength in iron superconductors

Abstract

Electronic correlations were long suggested not only to be responsible for the complexity of many novel materials, but also to form essential prerequisites for their intriguing properties. Electronic behavior of iron-based superconductors is far from conventional, while the reason for that is not yet understood. Here we present a combined study of the electronic spectrum in the iron-based superconductor FeSe by means of angle-resolved photoemission spectroscopy (ARPES) and dynamical mean field theory (DMFT). Both methods in unison reveal strong deviations of the spectrum from single-electron approximation for the whole 3$d$ band of iron: not only the well separated coherent and incoherent parts of the spectral weight are observed, but also a noticeable dispersion of the lower Hubbard band (LHB) is clearly present. This way we demonstrate correlations of the most puzzling intermediate coupling strength in iron superconductors.