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

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48 Chapter 4. Evolution of Electronic States in the Kondo Alloy ... Figure 4.3: Magnetic contributions to the specific heat of Yb1−xLuxB12 [4.6]. measurements and ∼ 3.5×10−10 Torr for the synchrotron radiation measurements. The sample surfaces were repeatedly scraped in situ with a diamond file. 4.3 Results and Discussion Figure 4.4 shows the entire valence-band spectra of Yb0.5Lu0.5B12 and YbB12 (Ref. [4.4]) and their difference spectrum. For the photon energy of 125 eV used here, the Yb and Lu 4f photoionization cross-sections are dominant [4.13]. Signals from Yb consist of two structures characteristic of valence fluctuating Yb compounds: divalent (4f 14 → 4f 13 ) and trivalent (4f 13 → 4f 12 ) parts. The divalent part is further decomposed into surface and bulk components [4.4, 14, 15] as shown in the Fig. 4.5. The bulk-surface 4f level shift increases by about 0.1 eV in going from YbB12 to Yb0.5Lu0.5B12. For Yb0.5Lu0.5B12, signals from the Lu 4f 14 → 4f 13 transition overlap the trivalent Yb signal. Prior to subtraction, the two spectra were normalized to the trivalent Yb signal intensity so that no Yb trivalent signal appeared in the difference spectrum. In the difference spectrum, in addition to the prominent doublets from the bulk and surface Lu atoms one can see residual divalent signals of bulk and surface Yb atoms near EF , indicating that the Lu-substitution causes a decrease of the Yb valence. Since the bulk residual signal amounts to ∼ 30% of the bulk divalent signal in YbB12, the Yb valence in Yb0.5Lu0.5B12 is estimated to be ∼ 2.82 compared with Yb valence ∼ 2.86 in YbB12 [4.4].
4.3. Results and Discussion 49 Intensity hν = 125 eV Lu 3+ 4f 14 → 4f 13 Yb 3+ 4f 13 → 4f 12 surface Yb 0.5 Lu 0.5 B 12 YbB 12 Yb 2+ 4f 14 → 4f 13 surface bulk difference bulk 12 8 4 0 Binding Energy (eV) Figure 4.4: Upper panel: valence-band photoemission spectra of Yb0.5Lu0.5B12 and YbB12. Calculated multiplet structures [4.16] are also shown by vertical bars. Lower panel: the difference spectrum between Yb0.5Lu0.5B12 and YbB12.
Page 1: Thesis High-Resolution Photoemissio
Page 4 and 5: ii CONTENTS 5.2 Experimental . . .
Page 6 and 7: 2 Chapter 1. Introduction Figure 1.
Page 8 and 9: 4 Chapter 1. Introduction Figure 1.
Page 10 and 11: 6 Chapter 1. Introduction peaks, wh
Page 12 and 13: 8 Chapter 1. Introduction only the
Page 14 and 15: 10 Chapter 1. Introduction directio
Page 16 and 17: 12 Chapter 1. Introduction activati
Page 18 and 19: 14 References [1.14] F. Iga, M. Kas
Page 21 and 22: Chapter 2 Photoemission Spectroscop
Page 23 and 24: 2.1. General Principles 19 Photoele
Page 25 and 26: 2.1. General Principles 21 where R(
Page 27 and 28: 2.2. Experimental 23 DOS Intensity
Page 29 and 30: 2.2. Experimental 25 Figure 2.5: Il
Page 31 and 32: 2.2. Experimental 27 baking out the
Page 33: References [2.1] O. Gunnarsson and
Page 36 and 37: 32 Chapter 3. Photoemission Study o
Page 48 and 49: 44 References the Kondo peak positi
Page 50 and 51: 46 Chapter 4. Evolution of Electron
Page 63 and 64: References [4.1] G. Aeppli and Z. F
Page 65: References 61 [4.25] P. Weibel,M. G
Page 68 and 69: 64 Chapter 5. Temperature Dependenc
Page 78 and 79: 74 References [5.10] N. Shimizu, F.
Page 81 and 82: Chapter 6 Substitution and Temperat
Page 83 and 84: 6.1. Introduction 79 Figure 6.2: Ma
Page 85 and 86: 6.3. Results and Discussion 81 6.3
Page 87 and 88: 6.3. Results and Discussion 83 DOS
Page 89 and 90: 6.3. Results and Discussion 85 dist
Page 91 and 92: 6.3. Results and Discussion 87 Apar
Page 93 and 94: 6.3. Results and Discussion 89 of E
Page 95 and 96: 6.3. Results and Discussion 91 the
Page 97: 6.4. Summary 93 and consistent anal
Page 100 and 101: 96 References [6.11] M. J. Rozenber
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98 Chapter 7. Temperature and Co-Su
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100 Chapter 7. Temperature and Co-S
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References [7.1] G. Aeppli and Z. F
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Chapter 8 Temperature and Al-Substi
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8.2. Experimental 113 and Fisk [8.2
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8.3. Results and Discussion 115 8.3
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8.3. Results and Discussion 117 Int
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8.3. Results and Discussion 119 dep
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8.3. Results and Discussion 121 σ
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8.4. Summary 123 temperature magnet
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126 References [8.14] T. Tonogai, A
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128 Chapter 9. Conclusion has shown
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130 Chapter 9. Conclusion (a) FeSi
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132 Chapter 9. Conclusion developed
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