Pre-edges in oxygen $(1s)$ x-ray absorption spectra: A spectral indicator for electron hole depletion and transport blocking in iron perovskites

The $eg↑/(t2g↓+eg↓)$ band ratio in cation-substituted La–Fe oxides is identified in $O(1s)$ x-ray absorption spectra as a linear spectral indicator for conducting electron holes. The $t2g↓$ and $eg↓$ bands act as a conductivity inhibitor by ferromagnetic double exchange coupling on the $eg↑$ electron. Disorder induced by substitution appears to modulate the hole conduction such that an exponential relation is found between the conductivity and the $eg↑/(t2g↓+eg↓)$ ratio and hole concentration. The quantitative correlation of conductivity and x-ray absorption spectra from heterovalent-substituted $LaFeO3$ lets substitution-driven metal insulator transitions appear in a new light.