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

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86 Chapter 6. Substitution and Temperature Dependence of the Conduction ... at about − 10 meV than at EF in the FD-function-divided spectra might lead one to doubt the calibration of the temperature, the Gauss width, and/or the background signal which is caused by excitation of the satellite resonance lines. Therefore, we have deduced the spectral DOS of LuB12 using another method as shown in Fig. 6.7; where we have reversed the energy scale of a spectrum with respect to EF and added it to the original spectrum [6.10]. For this method, precise information about the measurement temperature and the instrumental resolution is not needed3 while asymmetry between the occupied and unoccupied states is neglected. This analysis has revealed again the increase in the spectral DOS with temperature between EF and − 100 meV and the strongest temperature dependence occurring at ∼−10 meV rather than at EF . Nevertheless, the temperature dependence of the spectral DOS of LuB12 and that of YbB12 is qualitatively different: The sharp depression of the DOS at EF is present in YbB12 but is absent in LuB12. DOS LuB 12 YbB 12 300 K 7 K 300 K 7 K -150 -100 -50 0 Energy relative to E F (meV) Figure 6.7: Temperature-dependent spectral DOS deduced by adding the photoemission spectra and “reversed” spectra. For each sample, T = 7 K (thick curve), 75 K, 150 K, 225 K, and 300 K from bottom. 3 Also, the slope of the background is cancelled in this method.
6.3. Results and Discussion 87 Apart from the temperature dependence, the line shape of the spectral DOS itself is also unexpected. Band-structure calculation for LuB12 [6.9] has given a DOS of a weakly positive slope as shown in Fig. 6.8, which is almost flat around EF on the energy scale discussed here. On the other hand, the spectral DOS shows a strongly negative slope. 4 DOS (states/eV) 2.5 2.0 1.5 1.0 0.5 LuB 12 B p Lu d Lu f 0 -1.5 -1.0 -0.5 0 0.5 Energy relative to EF (eV) Figure 6.8: Calculated B p and Lu d, f partial DOS of LuB12 [6.9]. In the FD-function-divided spectra, we can also study part of the unoccupied states. In the lower panel of Fig. 6.6, the slope of the spectral DOS at higher temperature around and above EF is zero or positive, different from that below EF . To understand the discrepancy between the photoemission spectra and the band-structure calculation as well as the unusual temperature dependence of the spectral DOS, we can assume a V-shaped spectral DOS in LuB12 as the simplest scenario: Since electron correlation would be important also in the B sp band, the spectral DOS at EF may be suppressed in comparison with the DOS calculated within the one-electron approximation. At higher temperature, the sharp cusp-like spectral DOS at EF would be gradually smeared out due to various temperature-induced excitations including phonons. 4 The extrapolated linear DOS crosses the base line at 170 meV above EF , too inclined to compare with the calculated DOS.
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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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34 Chapter 3. Photoemission Study o
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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
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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
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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Page 127: 8.4. Summary 123 temperature magnet
Page 130 and 131: 126 References [8.14] T. Tonogai, A
Page 132 and 133: 128 Chapter 9. Conclusion has shown
Page 134 and 135: 130 Chapter 9. Conclusion (a) FeSi
Page 136: 132 Chapter 9. Conclusion developed
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