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

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Chapter 5 Temperature Dependence of the High-Resolution Photoemission Spectra of the Kondo Insulator YbB12 We have performed a detailed temperature-dependent photoemission study of the conductionband states in the Kondo insulator YbB12 using single crystalline samples. Measurements with improved energy resolution have revealed (pseudo)gaps of two energy scales. The size of the narrower gap ∼ 10 meV and its disappearance at high temperatures are consistent with the temperature dependence of the electrical resistivity and the magnetic susceptibility. The larger pseudogap of ∼ 100 meV depends on temperature even at room temperature. We discuss how the characteristics of the Kondo insulator are reflected in the conduction-band photoemission spectra. 5.1 Introduction The formation of a nonmagnetic insulating ground state in the Kondo insulator from a higher-temperature metallic state, where itinerant electrons are scattered by local moments, is one of the most intriguing phenomena in strongly correlated systems [5.1]. Among them YbB12 is the only Yb-based Kondo insulator [5.2]. In Yb compounds, because a large part of the 4f density of states (DOS) is on the occupied side of the Fermi level (EF ) in contrast to Ce compounds, one can study the main part of 63
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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
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 69 and 70: 5.2. Experimental 65 and then rapid
Page 71 and 72: 5.3. Results and Discussion 67 Inte
Page 73 and 74: 5.3. Results and Discussion 69 Figu
Page 75 and 76: 5.3. Results and Discussion 71 cent
Page 77 and 78: References [5.1] G. Aeppli and Z. F
Page 79: References 75 [5.22] K. Breuer, S.
Page 82 and 83: 78 Chapter 6. Substitution and Temp
Page 99 and 100: References [6.1] T. Susaki, T. Koni
Page 101 and 102: Chapter 7 Temperature and Co-Substi
Page 103 and 104: 7.1. Introduction 99 Figure 7.1: In
Page 105 and 106: 7.3. Results and Discussion 101 lig
Page 107 and 108: 7.3. Results and Discussion 103 Int
Page 109 and 110: 7.3. Results and Discussion 105 DOS
Page 111: 7.4. Summary 107 7.4 Summary To con
Page 114 and 115: 110 References [7.12] H. Ohta, S. K
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112 Chapter 8. Temperature and Al-S
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References [8.1] J.-J. Yeh and I. L
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Chapter 9 Conclusion We have studie
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low-temperature and low-energy elec
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Acknowledgments The present Thesis
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