Donut-shaped orbitals and Ising magnetism in Ca3Co2O6
The research teams of Hao Tjeng from the MPI-CPfS, Andrea Severing from the University of Cologne, Antoine Maignan from CRISMAT Laboratory Caen, and Maurits Haverkort from the University of Heidelberg have succeeded in determining the electronic orbital that is responsible for the Ising magnetism in Ca3Co2O6. A direct image of the donut-shaped orbital has been made using the new Max Planck end-station at German Electron Synchrotron DESY in Hamburg.
Here, the Max-Planck/Cologne/Caen/Heidelberg team made use of a purely experimental method to determine the electronic state that is responsible for the Ising magnetism in Ca3Co2O6. The method is called “s-core-level non-resonant inelastic x-ray scattering” (s-NIXS). It is a very new method and is extremely powerful since it provides a direct image of the relevant local electronic orbital. The first publication about this method is given in Ref. 1. The s-NIXS experiments on Ca3Co2O6 have been performed at the P01 beamline at PETRA III at DESY by Brett Leedahl and colleagues. The results have now appeared in Nature Communications . The orbital images obtained allowed for the unambiguous determination of the valence, spin, and orbital states for the two environments of Co ions present in the material. See Figure 1.
 H. Yavaş, M. Sundermann, K. Chen, A. Amorese, A. Severing, H. Gretarsson, M.W. Haverkort, L.H. Tjeng, Nature Physics 15, 559 (2019), https://doi.org/10.1038/s41567-019-0471-2.
 B. Leedahl, M. Sundermann, A. Amorese, A. Severing, H. Gretarsson, L.-Y. Zhang, A.C. Komarek, A. Maignan, M.W. Haverkort, and L.H. Tjeng, Nature Communications (2019), 15, 559–562 (2019), https://doi.org/10.1038/s41467-019-13273-4.