Photoemission Study of Substitution Effects on the Conduction-Band States in the Kondo Insulator YbB_<12> : Condensed Matter: Electronic Properties, etc.

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We have studied the substitution and temperature dependences of the B sp-Yb d-derived conduction-band states in Yb_<1-x>Lu_xB_<12> (x = 0.25, 0.50, 0.75, and 1.00) by high-resolution photoemission spectroscopy. As the Yb content increases, the density of states (DOS) between the Fermi level (E_F) and ~ - 20 meV is reduced while a broad peak grows at ~ -80 meV. The DOS reduction is considerably weakened at high temperatures (> ~100 K), consistent with the gap formation in YbB_<12> only at low temperatures. The temperature dependence of the DOS near E_F gradually becomes stronger with decreasing x but is abruptly enhanced below x = 0.25-0.50, showing the crucial contribution of Yb-Yb intersite interaction to the gap formation in YbB_<12>. The ~ -80 meV peak survives up to large x, indicating that it is caused by a single-impurity effect.
社団法人日本物理学会の論文
2001-03-15