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

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70 Chapter 5. Temperature Dependence of the High-Resolution Photoemission ... states has been shown to affect the conduction-band states over a wide (∼ 40 meV) energy range in the study of Yb1−xLuxB12 [5.6] Intensity DOS YbB 12 hν = 21.2 eV 305 K 225 K 150 K 75 K 6 K 305 K 225 K 150 K 75 K 6 K -150 -100 -50 0 50 100 Energy relative to E F (meV) Figure 5.4: Top: High-resolution photoemission spectra of YbB12 near EF (hν = 21.2 eV). Bottom: Spectral DOS at each temperature (thick curve) together with the DOS at 305 K (thin curve). The bottom line is the zero for the DOS at 6 K and the other densities of states have been offset. Recently, Breuer et al. [5.22] reported the non-f photoemission spectra of another Kondo insulator Ce3Bi4Pt3 (Tmax ∼ 80 K and ∆act ∼ 4 meV) in comparison with a Kondo metal CeSi2. The spectrum of Ce3Bi4Pt3 showed a shallow dip of ∼ 20 meV around EF and the spectrum of CeSi2 was identical to a simple Fermi edge. Very re-
5.3. Results and Discussion 71 cently, it was found by Takeda et al. [5.23] that Ce3Bi4Pt3 exhibited a sharp depression of the DOS at EF as in the present case of YbB12. The magnitude of the depression is smaller than that of YbB12, corresponding to the weaker temperature dependence of the electrical resistivity in Ce3Bi4Pt3[5.24]. DOS σ (mΩ -1 cm -1 ) 1.0 0.9 0.8 0.7 0.6 10 8 6 4 2 0 0 50 100 150 T (K) YbB 12 200 -100 meV -50 meV -20 meV -10 meV -0 meV Figure 5.5: Top: spectral DOS of YbB12 at several energy positions as a function of temperature. Bottom: electrical conductivity of the same sample as a function of temperature. In Fig. 5.5 the spectral DOS at several energies are plotted as a function of temperature and are compared with the dc electrical conductivity. All the intensities are normalized at 305 K. A decrease in the intensity from 75 K to 6 K, which is expected from the dc conductivity, is present only in the vicinity (within ∼ 10 meV) of EF .For 250 300
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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
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
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Page 93 and 94: 6.3. Results and Discussion 89 of E
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Page 97: 6.4. Summary 93 and consistent anal
Page 100 and 101: 96 References [6.11] M. J. Rozenber
Page 102 and 103: 98 Chapter 7. Temperature and Co-Su
Page 104 and 105: 100 Chapter 7. Temperature and Co-S
Page 113 and 114: References [7.1] G. Aeppli and Z. F
Page 115 and 116: Chapter 8 Temperature and Al-Substi
Page 117 and 118: 8.2. Experimental 113 and Fisk [8.2
Page 119 and 120: 8.3. Results and Discussion 115 8.3
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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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