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Abstract

We investigate the electronic structure of LaCoO3 across the gradual spin-state and insulator-to-metal transitions using bulk-sensitive hard x-ray photoelectron and soft x-ray absorption spectroscopies. The spectra exhibit strong variations with temperature. The energy gap is reduced by about 0.6 eV in going from 80 to 650 K but the near Fermi level intensity remains small, classifying LaCoO3 as a bad metal even in the metallic phase. We are able to explain the spectra in terms of incoherent sums of low-spin and high-spin Co3+ spectra. We also find that the energy parameters for the two Co sites are very different, revealing that paramagnetic LaCoO3 is a highly inhomogeneous system with local lattice relaxations that are spin-state-specific. This, in turn, provides a natural explanation for the much-debated temperature dependence of the activation energy for the transitions. © 2023 authors. Published by the American Physical Society. Published by the American Physical Society under the terms of the "https://creativecommons.org/licenses/by/4.0/"Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Open access publication funded by the Max Planck Society.