Electronic Band Structure of the Pyrochlore Ruthenium Oxides A_2Ru_2O_7(A=Bi, Tl and Y) : Condensed Matter: Electronic Properties, etc.

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A local-density electronic-band-structure calculation was performed for pyrochlore ruthenium oxides A_2Ru_2O_7 (A=Bi, Tl and Y). As a general feature, these pyrochlores have band structure composed of antibonding states of Ru 4d (t_<2g>) and O 2p orbitals near the Fermi energy (E_F) analogous to the layered perovskite superconductor Sr_2RuO_4. It was found that effects of A ion's orbitals to the band structure near E_F are quite important in the pyrochlores. Specifically in Tl_2Ru_2O_7, bands which consist of antibonding states of Tl 6l and O 2p orbitals exist with nearly half-fillings. A tight-binding model shows an energy-gap formation of the Tl-O bands with an orthorhombic lattice distortion. The calculated result suggests importance of coupling between electronic and lattice instabilities, which may be a clue to understand metal-insulator transition observed in Tl_2Ru_2O_7.
社団法人日本物理学会の論文
2000-02-15