Regensburg 2022 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 39: Correlated Electrons: Charge Order

TT 39.7: Vortrag

Freitag, 9. September 2022, 12:45–13:00, H23

Understanding the transition from metal to Hund’s insulator in CaFeO₃ — •Maximilian Merkel and Claude Ederer — Materials Theory Group, ETH Zürich, Switzerland

Materials where strong correlations are caused by the Hund’s interaction have recently attracted a lot of attention. In some cases, a dominant Hund’s interaction can even lead to the emergence of a charge-disproportionated insulating (CDI) or "Hund’s insulating" state. One example is the perovskite transition-metal oxide CaFeO₃ (CFO), which exhibits a transition from metal to Hund’s insulator around room temperature. This transition couples to a structural distortion that creates alternating large and small FeO₆ octahedra, leading to two inequivalent Fe sites with nominal Fe⁵⁺ and Fe³⁺ charge states. We study CFO using density functional theory (DFT) and dynamical mean-field theory (DMFT). To characterize the CDI state, we first apply DMFT to a five-orbital Hubbard model applicable to CFO and demonstrate the emergence of the CDI phase here [1]. We then investigate the energetics of the transition using fully self-consistent DFT+DMFT calculations. We discuss the ligand-hole character of the charge disproportionation due to the zero or even negative charge-transfer energy. Our calculations show that both structural and electronic properties of the CDI state are well described within DFT+DMFT but also that the subtle interplay of several effects represents a big challenge for any quantitative, predictive theory.

[1] M. E. Merkel and C. Ederer, Phys. Rev. B 104, 165135 (2021)