We have performed photoemission and soft x-ray absorption studies of pyrochlore-type Ru oxides, namely, the filling-control system Sm2-x Cax Ru2 O7 and the bandwidth-control system Sm2-x Bix Ru2 O7, which show insulator-to-metal transition with increasing Ca and Bi concentration, respectively. Core levels and the O 2p valence band in Sm2-x Cax Ru2 O7 show almost the same amount of monotonous upward energy shifts with Ca concentration, which indicates that the chemical potential is shifted downward due to hole doping. The Ru 4d band in Sm2-x Cax Ru2 O7 is also shifted toward the Fermi level (EF) with hole doping and the density of states (DOS) at EF increases. The core levels in Sm2-x Bix Ru2 O7, on the other hand, do not show clear energy shifts except for the Ru 3d core level, whose line shape change also reflects the increase of metallic screening with Bi concentration. We observe pronounced spectral weight transfer from the incoherent to the coherent parts of the Ru 4d t2g band with Bi concentration, which is expected for a bandwidth-control Mott-Hubbard system. The increase of the DOS at EF is more abrupt in the bandwidth-control Sm2-x Bix Ru2 O7 than in the filling-control Sm2-x Cax Ru2 O7, in accordance with a recent theoretical prediction. Effects of charge transfer between the Bi 6sp band and the Ru 4d band are also discussed.
|ジャーナル||Physical Review B - Condensed Matter and Materials Physics|
|出版ステータス||Published - 2006|
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