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

The long search for materials carrying quantum spin liquid states has recently led to $\ensuremath{\alpha}$-RuCl${}_{3}$, a layered honeycomb Mott insulator with substantial spin-orbit coupling. Often, controlled doping of materials with strong 2D character generates new exotic properties as well as a better understanding of the parent compound. This paper shows that the intercalation compound K${}_{0.5}$RuCl${}_{3}$ sustains a peculiar charge disproportionation into formally Ru${}^{2+}$ and Ru${}^{3+}$. Every Ru${}^{3+}$ with one hole in the t${}_{2g}$ shell is surrounded by Ru${}^{2+}$ where the t${}_{2g}$ level is full and magnetically inert. Thus each type of Ru sites forms a triangular lattice and nearest-neighbor interactions of the original honeycomb are blocked.