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Open Access Publications from the University of California

Hallmarks of Hunds coupling in the Mott insulator Ca2RuO4.

  • Author(s): 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, T-R
  • Jeng, H-T
  • Jozwiak, C
  • Bostwick, A
  • Rotenberg, E
  • Georges, A
  • Neupert, T
  • Chang, J
  • et al.

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.

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