5 years ago

Hallmarks of Hunds coupling in the Mott insulator Ca2RuO4

Hallmarks of Hunds coupling in the Mott insulator Ca2RuO4
M. Kim, Y. Sassa, E. Rotenberg, J. Chang, T. K. Kim, H. M. Rønnow, D. Sutter, C. G. Fatuzzo, S. Moser, F. Cossalter, M. Grioni, A. Bostwick, T-R Chang, N. C. Plumb, H-T Jeng, C. Jozwiak, A. Georges, V. Granata, T. Neupert, M. Shi, C. E. Matt, R. Fittipaldi, A. Vecchione, G. Gatti, M. Hoesch
A paradigmatic case of multi-band Mott physics including spin-orbit and Hund’s coupling is realized in Ca2RuO4. 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 Ca2RuO4 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 stabilization of the dxy orbital due to c-axis contraction is shown to be essential to explain the insulating phase. These results underscore the importance of multi-band physics, Coulomb interaction and Hund’s coupling that together generate the Mott insulating state of Ca2RuO4.

Publisher URL: http://www.nature.com/articles/ncomms15176

DOI: 10.1038/ncomms15176

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