Weak magnetism and the Mott-state of vanadium in superconducting Sr2VO3FeAs

TL;DR

This study combines neutron scattering and DFT calculations to analyze the magnetic and electronic properties of Sr2VO3FeAs, revealing weak V-magnetism, a Mott state of V, and a typical iron-arsenide Fermi surface.

Contribution

It demonstrates that Sr2VO3FeAs has a Mott-state V sublattice with weak magnetism and retains a quasi-nested Fermi surface, challenging previous predictions of strong magnetic ordering.

Findings

Weak magnetic ordering in V-sublattice at ~45 K.

V atoms are in a Mott-state with electronic correlations dominated by Coulomb repulsion.

The Fermi surface remains quasi-nested despite weak V magnetism.

Abstract

We report neutron scattering data and DFT calculations of the stoichiometric iron-arsenide superconductor Sr2VO3FeAs. Rietveld refinements of neutron powder patterns confirm the ideal composition without oxygen deficiencies. Experiments with polarized neutrons prove weak magnetic ordering in the V-sublattice of Sr2VO3FeAs at ~ 45 K with a probable propagation vector q = (1/8,1/8,0). The ordered moment of ~ 0.1 muB is too small to remove the V-3d bands from the Fermi level by magnetic exchange splitting, and much smaller than predicted from a recent LDA+U study. By using DFT calculations with a GGA+EECE functional we recover the typical quasi-nested Fermi-surface even without magnetic moment. From this we suggest that the V-atoms are in a Mott-state where the electronic correlations are dominated by on-site Coulomb-repulsion which shifts the V-3d states away from the Fermi energy. Our results are consistent with photoemission data and clearly reveal that Sr2VO3FeAs is a typical iron-arsenide superconductor with quasi-nested hole- and electron-like Fermi surface sheets, and constitutes no new paradigm. We suggest that intrinsic electron-doping through V3+/V4+ mixed valence is responsible for the absence of SDW ordering.