Successive Phase Transitions in Na_0.5CoO₂ based on the Triangular Lattice d-p Model

2008/10/14 by Yamakawa, Youichi, Ōno, Yoshiaki
#FOS: Physical sciences #Strongly Correlated Electrons (cond-mat.str-el)

paper · doi:10.48550/arxiv.0810.2380

Abstract

We investigate the electronic states of the CoO₂ plane in the layered cobalt oxides Na_0.5CoO₂ using the realistic 11 band d-p model on a two-dimensional triangular lattice. Effects of the Coulomb interaction on a Co site: the intra- and inter-orbital direct terms U and U', the exchange coupling J and the pair-transfer J', are treated within the Hartree-Fock approximation. It is found that the metallic antiferromagnetism takes place below T_c1 and, in addition, the orbital order accompanied by the small charge order takes place below T_c2 (< T_c1) where the system becomes insulator. The obtained results are consistent with the successive phase transitions observed in Na_0.5CoO₂.

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