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 CaRuO. 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 CaRuO 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 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 orbital due to -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 CaRuO. These results underscore the importance of Hund's coupling in the ruthenates and related multiband materials.
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Cite
@article{arxiv.1610.02854,
title = {Hallmarks of Hund's coupling in the Mott insulator Ca$_2$RuO$_4$},
author = {D. Sutter and C. G. Fatuzzo and S. Moser and M. Kim and R. Fittipaldi and A. Vecchione and V. Granata and Y. Sassa and F. Cossalter and G. Gatti and M. Grioni and H. M. Ronnow and N. C. Plumb and C. E. Matt and M. Shi and M. Hoesch and T. K. Kim and T. R. Chang and H. T. Jeng and C. Jozwiak and A. Bostwick and E. Rotenberg and A. Georges and T. Neupert and J. Chang},
journal= {arXiv preprint arXiv:1610.02854},
year = {2017}
}