Electronic structure of negative charge transfer CaFeO3 across the metal-insulator transition
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2018-01-30Author
Rogge, PCChandrasena, RU
Cammarata, A
Green, RJ
Shafer, P
Lefler, BM
Huon, A
Arab, A
Arenholz, E
Lee, HN
Lee, TL
Nemšák, S
Rondinelli, JM
Gray, AX
May, SJ
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http://hdl.handle.net/20.500.12613/4801
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10.1103/PhysRevMaterials.2.015002Abstract
© 2018 American Physical Society. 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 sites undergo no observable spectroscopic 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.Citation to related work
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http://dx.doi.org/10.34944/dspace/4783