Evidence for weak electronic correlations in Fe-pnictides

TL;DR

This study uses x-ray techniques to analyze charge dynamics in Fe pnictides, revealing that electronic correlations are weak and similar to metallic Fe, contrasting with strongly correlated cuprates.

Contribution

It provides experimental and theoretical evidence that Coulomb correlations in Fe pnictides are weak, emphasizing metallicity and covalency over strong electronic interactions.

Findings

XAS and RIXS spectra resemble Fe metal

Coulomb correlations are smaller than in cuprates

Hubbard U is approximately 2 eV or less

Abstract

Using x-ray absorption and resonant inelastic x-ray scattering, charge dynamics at and near the Fe $L$ edges is investigated in Fe pnictide materials, and contrasted to that measured in other Fe compounds. It is shown that the XAS and RIXS spectra for 122 and 1111 Fe pnictides are each qualitatively similar to Fe metal. Cluster diagonalization, multiplet, and density-functional calculations show that Coulomb correlations are much smaller than in the cuprates, highlighting the role of Fe metallicity and strong covalency in these materials. Best agreement with experiment is obtained using Hubbard parameters $U\lesssim 2$eV and $J\approx 0.8$eV.