Temperature induced in-gap states in the band structure and the insulator-metal transition in LaCoO3

S. Ovchinnikov; Yu. Orlov; I. Nekrasov; Z. Pchelkina

paper

Temperature induced in-gap states in the band structure and the insulator-metal transition in LaCoO3

arXiv:1005.1732

Abstract

For many years a spin-state transition at $T \approx 100 K$ and insulator - metal transition (IMT) at $T_{I M T} \approx 600 K$ in LaCoO $_{3}$ remains a mystery. Small low-spin - high-spin spin gap $Δ_{S} = E (H S) - E (L S) \sim 100 K$ results in the spin-state transition. The large charge gap $2 E_{a} \approx 2300 K$ ( $E_{a}$ is the activation energy) vs. $Δ_{S}$ and $T_{I M T}$ implies that LaCoO $_{3}$ is not a simple narrow-gap semiconductor. Here we explain both the spin-state and IMT on the same footing. We obtain strong temperature dependent band structure in LaCoO $_{3}$ by the LDA+GTB method that incorporates strong electron correlations, covalence and spin-orbital interaction exactly inside the CoO $_{6}$ cluster and the interclaster hopping between different multielectron configurations by perturbation theory for Hubbard X-operators.