Electronic and crystal structures of LnFeAsO1-xHx (Ln = La, Sm) studied by x-ray absorption spectroscopy, x-ray emission spectroscopy, and x-ray diffraction (part I: carrier-doping dependence)

A carrier doping by a hydrogen substitution in LaFeAsO1-x H (x ) is known to cause two superconducting (SC) domes with the magnetic order at both end sides of the doping. In contrast, SmFeAsO1-x H (x ) has a similar phase diagram but shows single SC dome. Here, we investigated the electronic and crystal structures for iron oxynitride LnFeAsO(1-x ) H (x ) (Ln = La, Sm) with the range of x = 0-0.5 by using x-ray absorption spectroscopy, x-ray emission spectroscopy, and x-ray diffraction. For both compounds, we observed that the pre-edge peaks of x-ray absorption spectra near the Fe-K edge were reduced in intensity on doping. The character arises from the weaker As-Fe hybridization with the longer As-Fe distance in the higher doped region. We can reproduce the spectra near the Fe-K edge according to the Anderson impurity model with realistic valence structures using the local-density approximation (LDA) plus dynamical mean-field theory (DMFT). For Ln = Sm, the integrated-absolute difference (IAD) analysis from x-ray Fe-K beta emission spectra increases significantly. This is attributed to the enhancement of magnetic moment of Fe 3d electrons stemming from the localized picture in the higher doped region. A theoretical simulation implementing the self-consistent vertex-correction method reveals that the single dome superconducting phase for Ln = Sm arises from a better nesting condition in comparison with Ln = La.

Automated summary

The electronic and crystal structures of LnFeAsO (1-x) H (x) (Ln = La, Sm) compounds were investigated, revealing a reduction in intensity of pre-edge peaks near the Fe-K edge on doping, attributed to weaker As-Fe hybridization. The analysis of integrated-absolute difference (IAD) showed a significant increase in Sm, indicating enhanced magnetic moment of Fe 3d electrons in the higher doped region, contributing to the single dome superconducting phase in Sm.