Thesis High-Resolution Photoemission Study of Kondo Insulators ...

Chapter 6
Substitution and Temperature
Dependence of the Conduction
Band in Yb1−xLuxB12
We have studied the temperature dependence of the B p-derived conduction band in
Yb1−xLuxB12 (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 (EF ) and ∼−20 meV is depressed and simultaneously a broad peak grows at ∼−
80 meV. Such substitution dependence is considerably weakened at higher temperature,
indicating a decoupling between the f electrons and the conduction electrons at high
temperatures. The temperature-dependent depression near EF is abruptly enhanced
for small x, showing an effect beyond the single-site mechanism in the gap formation
of YbB12.
6.1 Introduction
In the preceding Chapters we have shown that the gap in YbB12 vanishes with Lu
substitution (Chap. 4) [6.1] or with temperature (Chap. 5) [6.2]. In this Chapter we
present the results of a thorough temperature-dependent photoemission study of the
B sp Yb d-derived conduction band in Yb1−xLuxB12 (x = 0.25, 0.50, 0.75, and 1.00)
performed on single crystals. Transport and thermodynamic properties of Yb1−xLuxB12
single crystals [6.3, 4] are qualitatively the same as those of polycrystals [6.5]. We show
the electrical resistivity of Yb1−xLuxB12 single crystals [6.4] in Fig. 6.1. The activation-
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