Correlation effects in Ni 3d states of LaNiPO

TL;DR

This study combines experimental soft X-ray spectroscopy and theoretical LDA+DMFT calculations to reveal strong electron correlation effects in Ni 3d states of LaNiPO, including a lower Hubbard band, distinguishing it from related compounds.

Contribution

It provides the first detailed comparison of Ni 3d electron correlations in LaNiPO using combined experimental and theoretical approaches, highlighting the presence of a lower Hubbard band.

Findings

Ni 3d states are strongly renormalized and shifted lower in LaNiPO.

A lower Hubbard band at -9 eV is observed in LaNiPO, similar to NiO.

Stronger electron correlations are present in LaNiPO compared to LaFeAsO.

Abstract

The electronic structure of the new superconducting material LaNiPO experimentally probed by soft X-ray spectroscopy and theoretically calculated by the combination of local density approximation with Dynamical Mean-Field Theory (LDA+DMFT) are compared herein. We have measured the Ni L2,3 X-ray emission (XES) and absorption (XAS) spectra which probe the occupied and unoccupied the Ni 3d states, respectively. In LaNiPO, the Ni 3d states are strongly renormalized by dynamical correlations and shifted about 1.5 eV lower in the valence band than the corresponding Fe 3d states in LaFeAsO. We further obtain a lower Hubbard band at -9 eV below the Fermi level in LaNiPO which bears striking resemblance to the lower Hubbard band in the correlated oxide NiO, while no such band is observed in LaFeAsO. These results are also supported by the intensity ratio between the transition metal L2 and L3 bands measured experimentally to be higher in LaNiPO than in LaFeAsO, indicating the presence of the stronger electron correlations in the Ni 3d states in LaNiPO in comparison with the Fe 3d states in LaFeAsO. These findings are in accordance with resonantly excited transition metal L3 X-ray emission spectra which probe occupied metal 3d-states and show the appearance of the lower Hubbard band in LaNiPO and NiO and its absence in LaFeAsO.