Strength of correlations in pnictides and its assessment by theoretical calculations and spectroscopy experiments

TL;DR

This paper combines theoretical calculations and spectroscopy experiments to assess the correlation strength in pnictides, specifically LaFeAsO, revealing moderate electronic correlations consistent with experimental spectra.

Contribution

It applies LDA+DMFT calculations with first-principles parameters to evaluate correlation strength in LaFeAsO, bridging theory and spectroscopy data.

Findings

Moderate electron correlation with mass enhancement ~2.

Spectra agree with metallic iron, not Mott insulators.

Theoretical and experimental spectra are consistent.

Abstract

LDA+DMFT (Local Density Approximation combined with Dynamical Mean-Field Theory) computation scheme has been used to calculate spectral properties of LaFeAsO -- the parent compound of the new high-T_c iron oxypnictides. The average Coulomb repulsion U=3-4 eV and Hund's exchange J=0.8 eV parameters for iron 3d electrons were calculated using the first principles constrained density functional theory scheme in the Wannier functions formalism. DMFT calculations using these parameters result in moderately correlated electronic structure with effective electron mass enhancement m^*~2 that is in agreement with the experimental X-ray and photoemission spectra. Conclusion of moderate correlations strength is confirmed by the observation that pnictides experimental spectra agree well with corresponding spectra for metallic iron while being very different with Mott insulator FeO spectra.