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 are compared herein. We have measured the $\text{Ni}{L}_{2,3}$ x-ray emission and absorption spectra which probe the occupied and unoccupied $\text{Ni}3d$ states, respectively. In LaNiPO, the $\text{Ni}3d$ states are strongly renormalized by dynamical correlations and shifted about 1.5 eV lower in the valence band than the corresponding $\text{Fe}3d$ states in LaFeAsO. We further obtain a lower Hubbard band at $-9\text{eV}$ 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 $L_2$ and $L_3$ bands measured experimentally to be higher in LaNiPO than in LaFeAsO, indicating the presence of the stronger electron correlations in the $\text{Ni}3d$ states in LaNiPO in comparison with the $\text{Fe}3d$ states in LaFeAsO. These findings are in accordance with resonantly excited transition metal $L_3$ 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.

• Received 18 April 2010

DOI:https://doi.org/10.1103/PhysRevB.81.235121