Structural analysis of honeycomb ruthenates - the relationship between the dimer formation and layer stacking pattern

Honeycomb ruthenates (Ru4+, 4d4) are the potential playground for exotic magnetism associated with strong spin-orbit coupling. However, the real honeycomb ruthenate Li2RuO3 shows dimerization of Ru atoms where spin and orbital degrees of freedom are quenched and spin-orbit coupling does not work. To suppress the dimerization, we employed ion-exchange technique on Li2RuO3 and obtained new materials such as Cu2RuO3 and H-Li2RuO3. Cu2RuO3 does not show dimerization and displays a Van Vleck-like magnetic susceptibility as expected for d4 system with spin-orbit coupling. The proton exchanged H-Li2RuO3 was found to be non-magnetic as in Li2RuO3, suggesting the presence of dimerization. To understand the relationship between the electronic ground state and crystal structure, we will perform structural analyses with high-resolution powder neutron diffractions on the new honeycomb ruthenates.