Magnetic ordering and structural transition in layered Li$_{2}$RuO$_{3}$*

Li$_{2}$RuO$_{3}$ is a layered, triangular-lattice metal oxide system much like Na$_{x}$CoO$_{2}$, NaNiO$_{2}$ and LiNiO$_{2}$ with the exception that one of every three transition metal ions (Ru) is replaced by a Li ion. This results in a honeycomb arrangement of spin-carrying ions and eliminates the magnetic frustration intrinsic to the triangular lattice. Here we investigate the electronic structure of Li$_{2}$RuO$_{3}$, especially in relation to its magnetic ordering both in-plane and between adjacent planes. We find that the dimerization of Ru atoms within the metal-oxide planes acts in conjunction with magnetic ordering to establish a gapped, magnetic ground state. The change in the energy level spectrum brought on by the formation of spin-polarized Ru-Ru molecular orbitals replaces the expected Jahn-Teller mechanism as a way of relieving a degeneracy at the Fermi energy.