α-RuCl3,a promising material to accomplish the Kitaev honeycomb model,has attracted enormous interest recently.Mottness and p-d bonds play vital roles in generating Kitaev interactions and underpinning the potential exotic states of quantum magnets,and the van der Waals monolayer is considered to be a better platform to approach a two-dimensional Kitaev model than the bulk.Here,we worked out the growth art of an α-RuCl3 monolayer on a graphite substrate and studied its electronic structure,particularly the delicate orbital occupations,through scanning tunneling microscopy and spectroscopy.An in-plane lattice expansion of 2.67 ± 0.83 is observed and the pronounced t_(2g)-pπ and eg-pσ hybridization are visualized.The Mott nature is unveiled by an ~0.6 eV full gap at the Fermi level located inside the t2g-pπ manifold which is further verified by the density functional theory calculations.The monolayer phase of α-RuCl3 fulfills the a priori criteria of recent theoretical predictions of tuning the relevant properties in this material and provides a novel platform to explore the Kitaev physics.
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