Nearest-neighbor Kitaev exchange blocked by charge order in electron-doped α-RuCl₃

A quantum spin liquid might be realized in α-RuCl₃, a honeycomb-lattice magnetic material with substantial spin-orbit coupling. Moreover, α-RuCl₃ is a Mott insulator, which implies the possibility that novel exotic phases occur upon doping. Here, we study the electronic structure of this material when intercalated with potassium by photoemission spectroscopy, electron energy loss spectroscopy, and density functional theory calculations. We obtain a stable stoichiometry at K_0.5RuCl₃. This gives rise to a peculiar charge is proportionation into formally Ru²⁺ (4d⁶) and Ru³⁺ (4d⁵). Every Ru 4d⁵ site with one hole in the t_2g shell is surrounded by nearest neighbors of 4d⁶ character, where the t_2g level is full and magnetically inert. Thus, each type of Ru site forms a triangular lattice, and nearest-neighbor interactions of the original honeycomb are blocked.