2018
DOI: 10.1103/physrevmaterials.2.015002
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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 t… Show more

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Cited by 38 publications
(38 citation statements)
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“…As seen in Fig. 4, off the Bragg condition the measured intensity has features that resemble an x-ray absorption spectrum of these ferrates, as expected, where the strong prepeak feature between 527.0-529.5 eV arises from the oxygen ligand holes due to the negative charge transfer energy [31,40,41]. At the Bragg condition, there is a clear enhancement of the intensity within the prepeak region only.…”
Section: Film Results Discussionsupporting
confidence: 78%
See 1 more Smart Citation
“…As seen in Fig. 4, off the Bragg condition the measured intensity has features that resemble an x-ray absorption spectrum of these ferrates, as expected, where the strong prepeak feature between 527.0-529.5 eV arises from the oxygen ligand holes due to the negative charge transfer energy [31,40,41]. At the Bragg condition, there is a clear enhancement of the intensity within the prepeak region only.…”
Section: Film Results Discussionsupporting
confidence: 78%
“…A decrease in the q vector implies that the real-space length of the helix increases or, analogously, the helical angle between neighboring (111) planes, φ, decreases. A previous theoretical study of the helical state in these ferrates found that the helical ordering arises due to the double exchange effect coupled with a negative charge transfer energy, ∆ [24,37], where a negative ∆ arises from the high formal oxidation state of Fe 4+ in these ferrates [30,31,38,39]. The helical angle tracks a single parameter δ = (ǫ F − ∆ + t pp )/(pdσ), where ǫ F is the Fermi level position, t pp is the oxygen-oxygen hopping amplitude, and pdσ is the σ hybridization between p and d orbitals.…”
Section: Film Results Discussionmentioning
confidence: 96%
“…Going further, we reveal that CO and OO compete in AFeO 3 compounds and we unveil the possibility to switch from CO-type to OO-type MIT in CaFeO 3 thin films under appropriate strain conditions. This offers a convincing explanation for the enormous resistivity at room-temperature recently found in CaFeO 3 films grown on SrTiO 3 [21].…”
supporting
confidence: 57%
“…Material Synthesis : Ferrate superlattices were deposited by oxygen‐assisted molecular beam epitaxy at ≈ 650 °C with a background oxygen pressure of 8 × 10 −6 Torr (base pressure 4 × 10 −10 Torr). The as‐grown sample was subsequently annealed by heating to ≈ 600 °C in oxygen plasma (200 W, 1 × 10 −5 Torr chamber pressure) and then slowly cooled to room temperature in oxygen plasma . Prior to all measurements, the films were re‐annealed in oxygen plasma by the same post‐growth process to mitigate oxygen deficiency.…”
Section: Methodsmentioning
confidence: 99%
“…These ferrate perovskites are strongly correlated materials that exhibit a metal–insulator transition and non‐collinear magnetism with multi‐ q topological spin structures . Their negative charge transfer energy results in a large self‐doped ligand hole contribution to their electronic structure such that the ground state is dominated by a configurational mixture of d 4 and d 5 L 1 , and the degree of ligand hole ( L 1 ) character is a measure of the FeO hybridization. While these ferrates have similar electronic structures, their crystal structures differ, where SrFeO 3 is cubic with 180° FeOFe bond angles and CaFeO 3 is orthorhombic with 158° bond angles .…”
mentioning
confidence: 99%