Jeff Description of the Honeycomb Mott Insulator α-RuCl3

Novel ground states might be realized in honeycomb lattices with strong spin-orbit coupling. Here we study the electronic structure of alpha-RuCl3, in which the Ru ions are in a d(5) configuration and form a honeycomb lattice, by angle-resolved photoemission, x-ray photoemission, and electron energy loss spectroscopy supported by density functional theory and multiplet calculations. We find that alpha-RuCl3 is a Mott insulator with significant spin-orbit coupling, whose low energy electronic structure is naturally mapped onto J(eff) states. This makes alpha-RuCl3 a promising candidate for the realization of Kitaev physics. Relevant electronic parameters such as the Hubbard energy U, the crystal field splitting 10 Dq, and the charge transfer energy Delta are evaluated.