Doping effects on the valence bond solid of Li${}_2$RuO${}_3$ with Mn substitution

Abstract

$L{i}_{2}Ru{O}_3$ with a honeycomb structure undergoes a drastic transition from a regular honeycomb lattice with the $C2/m$ space group to a valence bond solid state of the $P{2}_1/m$ space group with an extremely strong dimerization at 550 K. We synthesized $L{i}_{2}R{u}_{1-x}M{n}_x{O}_3$ with a full solid solution and investigated doping effects on the valence bond solid state as a function of Mn content. The valence bond solid state is found to be stable up to $x=0.2$, based on our extensive experiments: structural studies, resistivity, and magnetic susceptibility. On the other hand, the extended x-ray absorption fine structure analyses show that the dimer local structure remains robust even above $x=0.2$ with a minimal effect on the dimer bond length. This indicates that the locally-disordered dimer structure survives well into the Mn-rich phase even though the thermodynamically stable average structure has the $C2/m$ space group. Our results prove that the dimer formation in $L{i}_{2}Ru{O}_3$ is predominantly a local phenomenon driven by the formation of orbitally-assisted metal-metal bonds and that these dimers are relatively robust against doping-induced disorder.

15 pages, 5 figures