Electronic structure of negative charge transfer CaFeO3 across the metal-insulator transition

Abstract

We investigated the metal-insulator transition for epitaxial thin films of the perovskite CaFeO3, a material with a significant oxygen ligand hole contribution to its electronic structure. We find that biaxial tensile and compressive strain suppress the metal-insulator transition temperature. By combining hard X-ray photoelectron spectroscopy, soft X-ray absorption spectroscopy, and density functional calculations, we resolve the element-specific changes to the electronic structure across the metal-insulator transition. We demonstrate that the Fe electron valence undergoes no observable change between the metallic and insulating states, whereas the O electronic configuration undergoes significant changes. This strongly supports the bond-disproportionation model of the metal-insulator transition for CaFeO3 and highlights the importance of ligand holes in its electronic structure. By sensitively measuring the ligand hole density, however, we find that it increases by ~5-10% in the insulating state, which we ascribe to a further localization of electron charge on the Fe sites. These results provide detailed insight into the metal-insulator transition of negative charge transfer compounds and should prove instructive for understanding metal-insulator transitions in other late transition metal compounds such as the nickelates.

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Cited by in corpus (11)

• Hole-Induced Electronic and Optical Transitions in La1-xSrxFeO3 Epitaxial Thin Films
• From Charge to Orbital Ordered Metal-Insulator Transition in Alkaline-Earth Ferrites
• Itinerancy-dependent non-collinear spin textures in SrFeO3, CaFeO3, and CaFeO3/SrFeO3 heterostructures probed via resonant x-ray scattering
• Superconductivity in a layered cobalt oxychalcogenide Na${}_2$CoSe${}_2$O with a triangular lattice
• Negative charge transfer energy in correlated compounds
• Metal-insulator transition and local-moment collapse in negative charge-transfer CaFeO${}_3$ under pressure
• Inverted orbital polarization in strained correlated oxide films
• Calculation of screened Coulomb interaction parameters for the charge-disproportionated insulator CaFeO${}_3$
• Topotactic phase transformation in correlated vanadium dioxide through oxygen vacancy ordering
• Weak electronic correlations in the cobalt oxychalcogenide superconductor Na2CoSe2O
• Elastic stripes formation at electronic transitions