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

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92 Chapter 6. Substitution and Temperature Dependence of the Conduction ... Difference DOS (a) 300 K (b) x = 0.00 x = 0.25 x = 0.50 x = 0.75 x = 1.00 7 K -250-200-150-100-50 0 300 K 225 K 150 K 75 K 7 K -250-200-150-100-50 0 Energy relative to E F (meV) Figure 6.12: (a) Difference spectral DOS of Yb1−xLuxB12 relative to the spectral DOS of LuB12 at 7 K. All the DOS have been smoothed to the same extent. For each x, T = 7 K (thick curves), 75 K, 150 K, 225 K, and 300 K from bottom. (b) The same difference DOS as (a) showing the substitution dependence at each temperature. The thick solid curves represent the DOS of the x = 0 sample, the dashed curves x = 0.25, the solid curves x = 0.50, the dot-dashed curves x = 0.75, and the solid dashed curves x = 1.00.
6.4. Summary 93 and consistent analysis of both the 4f and conduction-band spectra would be highly desirable in future. 6.4 Summary We have studied the Lu-substitution dependence in the photoemission spectra of the B sp-derived conduction band in Yb1−xLuxB12 at various temperatures. The substitution dependence is most clearly present at 7 K, where in going from LuB12 to YbB12 the pseudogap of < 20 meV opens and a broad peak at ∼−80 meV evolves. Such substitution dependence is gradually smeared out with increasing temperature, indicating a decoupling between the f electrons and the conduction electrons above ∼ TK. The larger pseudogap of 0.1 eV, which has been observed in YbB12, is present for any x concentration including LuB12 but the sharp depression in the vicinity of EF is observed only for x ≤ 0.25. That the spectra for intermediate x’s cannot be reproduced by a 1 − x : x superposition of those of YbB12 and LuB12 indicates that the effect beyond the single-site description is important in the gap formation of YbB12.
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Thesis High-Resolution Photoemissio
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ii CONTENTS 5.2 Experimental . . .
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2 Chapter 1. Introduction Figure 1.
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4 Chapter 1. Introduction Figure 1.
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6 Chapter 1. Introduction peaks, wh
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8 Chapter 1. Introduction only the
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10 Chapter 1. Introduction directio
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12 Chapter 1. Introduction activati
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14 References [1.14] F. Iga, M. Kas
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Chapter 2 Photoemission Spectroscop
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2.1. General Principles 19 Photoele
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2.1. General Principles 21 where R(
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2.2. Experimental 23 DOS Intensity
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2.2. Experimental 25 Figure 2.5: Il
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2.2. Experimental 27 baking out the
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References [2.1] O. Gunnarsson and
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32 Chapter 3. Photoemission Study o
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Page 78 and 79: 74 References [5.10] N. Shimizu, F.
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Page 115 and 116: Chapter 8 Temperature and Al-Substi
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Page 127: 8.4. Summary 123 temperature magnet
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Page 134 and 135: 130 Chapter 9. Conclusion (a) FeSi
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