Anomalous High-Energy Electronic Interaction in Iron-Based Superconductor

TL;DR

This study reveals that the unusual band renormalization in iron-based superconductors stems from high-energy electronic interactions, involving coupling to excitations around 0.5 eV, which is distinct from typical metals.

Contribution

It demonstrates that the anomalous band renormalization is caused by high-energy interactions, providing new insight into the electronic behavior of iron-based superconductors.

Findings

Spectral weight depletion in Fe 3d band

Increased scattering rate at high energies

Coupling to excitations at ~0.5 eV explains anomalies

Abstract

Strong electron interactions in solids increase effective mass, and shrink the electronic bands [1]. One of the most unique and robust experimental facts about iron-based superconductors [2-4] is the renormalization of the conduction band by factor of 3 near the Fermi level [5-9]. Obviously related to superconductivity, this unusual behaviour remains unexplained. Here, by studying the momentum-resolved spectrum of the whole valence band in a representative material, we show that this phenomenon originates from electronic interaction on a much larger energy scale. We observe an abrupt depletion of the spectral weight in the middle of the Fe $3d$ band, which is accompanied by a drastic increase of the scattering rate. Remarkably, all spectral anomalies including the low-energy renormalization can be explained by coupling to excitations, strongly peaked at about 0.5 eV. Such high-energy interaction distinguishes all unconventional superconductors from common metals.