Hallmarks of Hund's coupling in the Mott insulator Ca${}_2$RuO${}_4$

Abstract

A paradigmatic case of multi-band Mott physics including spin-orbit and Hund's coupling is realised in Ca${}_2$RuO${}_4$. Progress in understanding the nature of this Mott insulating phase has been impeded by the lack of knowledge about the low-energy electronic structure. Here we provide -- using angle-resolved photoemission electron spectroscopy -- the band structure of the paramagnetic insulating phase of Ca${}_2$RuO${}_4$ and show how it features several distinct energy scales. Comparison to a simple analysis of atomic multiplets provides a quantitative estimate of the Hund's coupling $J=0.4$ eV. Furthermore, the experimental spectra are in good agreement with electronic structure calculations performed with Dynamical Mean-Field Theory. The crystal field stabilisation of the d${}_{xy}$ orbital due to $c$-axis contraction is shown to be important in explaining the nature of the insulating state. It is thus a combination of multiband physics, Coulomb interaction and Hund's coupling that generates the Mott insulating state of Ca${}_2$RuO${}_4$. These results underscore the importance of Hund's coupling in the ruthenates and related multiband materials.

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Cited by in corpus (67)

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• Bandwidth-control orbital-selective delocalization of 4f electrons in epitaxial Ce films
• Observation of spin-dependent dual ferromagnetism in perovskite ruthenates
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• Decomposing imaginary time Feynman diagrams using separable basis functions: Anderson impurity model strong coupling expansion
• Pattern Formation by Electric-field Quench in Mott Crystal
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• Resonant Inelastic X-ray Scattering Study of Ca${}_3$Ru${}_2$O${}_7$
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• Effects of paramagnetic fluctuations on the thermochemistry of MnO (100) surfaces in the oxygen evolution reaction
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• Magnetic polarons due to spin-length fluctuations in ${\mathbf{d}}^4$ spin-orbit Mott systems