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

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ii CONTENTS 5.2 Experimental . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64 5.3 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . 66 5.4 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72 6 Substitution and Temperature Dependence of the Conduction Band in Yb1−xLuxB12 77 6.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77 6.2 Experimental . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80 6.3 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . 81 6.3.1 Substitution Dependence at 7 K . . . . . . . . . . . . . . . . . . 81 6.3.2 Conduction Band in LuB12 . . . . . . . . . . . . . . . . . . . . . 83 6.3.3 Substitution and Temperature Dependence . . . . . . . . . . . . 88 6.4 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93 7 Temperature and Co-Substitution Dependence of the Photoemission Spectra of FeSi 97 7.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97 7.2 Experimental . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100 7.3 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . 101 7.4 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107 8 Temperature and Al-Substitution Dependence of the Photoemission Spectra of FeSi 111 8.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111 8.2 Experimental . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113 8.3 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . 115 8.4 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123 9 Conclusion 127
Chapter 1 Introduction 1.1 Kondo insulator and Kondo metal The appearance of Kondo effect in a Kondo-ion lattice and the formation of a heavy fermion by cooling it is one of the most profound manifestation of electron correlation in a system consisting of f and conduction electrons. More striking is the temperature dependence of a dozen of nonmagnetic semiconducting rare-earth compounds such as Ce3Bi4Pt3, CeNiSn, CeRhSb, and YbB12 [1.1, 2]. Anomalous magnetic susceptibilities and electrical resistivities of such semiconductors, i.e., Kondo insulators, are compared with those of Kondo metals in Fig. 1.1. In Kondo insulators, the Ce or Yb ions behave as local moments above the Kondo temperature (TK) and share high-temperature properties with Kondo metals. The magnetic susceptibility follows the Curie-Weiss law and the electrical resistivity is dominated by Kondo scattering resulting in the − log T behavior. In Kondo metals, as the temperature is lowered, the magnetic susceptibility reaches a constant value corresponding to an enhanced Pauli paramagnetism and the electrical resistivity decreases as T 2 , reflecting the formation of a heavy Fermi liquid. In Kondo insulators, however, on cooling down, the magnetic susceptibility rapidly decreases after showing a broad maximum and the electrical resistivity exhibits a sharp increase in an activation form. Reported Kondo insulators are collected in Table 1.1. A study of SmB6 has a long history since its semiconducting behavior was reported in 1969 [1.3]. Note that other trivalent rare-earth hexaborides are metallic and show magnetic orders at low temperatures. Then a narrow gap in YbB12 was reported in 1983 [1.4]. At that time, no Ce compound was reported as an intermediate-valent narrow-gap semiconductor and 1
Page 1: Thesis High-Resolution Photoemissio
Page 6 and 7: 2 Chapter 1. Introduction Figure 1.
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Page 14 and 15: 10 Chapter 1. Introduction directio
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Page 18 and 19: 14 References [1.14] F. Iga, M. Kas
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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
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50 Chapter 4. Evolution of Electron
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References [4.1] G. Aeppli and Z. F
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References 61 [4.25] P. Weibel,M. G
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64 Chapter 5. Temperature Dependenc
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74 References [5.10] N. Shimizu, F.
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6.3. Results and Discussion 81 6.3
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6.3. Results and Discussion 83 DOS
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6.4. Summary 93 and consistent anal
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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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