- Sutter, D
- Fatuzzo, CG
- Moser, S
- Kim, M
- Fittipaldi, R
- Vecchione, A
- Granata, V
- Sassa, Y
- Cossalter, F
- Gatti, G
- Grioni, M
- Rønnow, HM
- Plumb, NC
- Matt, CE
- Shi, M
- Hoesch, M
- Kim, TK
- Chang, TR
- Jeng, HT
- Jozwiak, C
- Bostwick, A
- Rotenberg, E
- Georges, A
- Neupert, T
- Chang, J
- et al.
© 2017 The Author(s). 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 Ca2RuO4and 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 d xy 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.