Orbital order in NaTiO2: A first principles study

The debate over the orbital order in the layered triangular lattice system NaTiO2 has been rekindled by the recent experiments of McQueen et al. [Phys. Rev. Lett. 101 (2008) 166402] on NaVO2. In view of this, the nature of orbital ordering, in both high and low temperature phases, is studied using an ab-initio electronic structure calculation. The orbital order observed in our calculations in the low temperature structure of NaTiO2 is consistent with the predictions of McQueen et al. An LDA plus dynamical mean-field calculation shows considerable transfer of spectral weight from the Fermi level but no metal–insulator transition, confirming the poor metallic behavior observed in transport measurements.

► NaTiO2 is metallic in both rhombohedral and monoclinic phases.
► Coulomb correlation (in LSDA+U ) does not make the system insulating.
► Low temperature monoclinic phase has been observed to be orbitally ordered.
► Orbital order is found to be consistent with the predictions of McQeen et al.
► LDA+DMFT recovers the bad metallic state observed in experiments.