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

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96 References [6.11] M. J. Rozenberg, G. Kotliar, and H. Kajueter, Phys. Rev. B 54, 8452 (1996). [6.12] T. Susaki, A. Sekiyama, K. Kobayashi, T. Mizokawa, A. Fujimori, M. Tsunekawa, T. Muro, T. Matsushita, S. Suga, H. Ishii, T. Hanyu, A. Kimura, H. Namatame, M. Taniguchi, T. Miyahara, F. Iga, M. Kasaya, and H. Harima, Phys. Rev. Lett. 77, 4269 (1996).
Chapter 7 Temperature and Co-Substitution Dependence of the Photoemission Spectra of FeSi We have studied the effect of varying temperature and Co substitution on the lowenergy electronic structure of FeSi by photoemission spectroscopy. We have observed that the density of states (DOS) of FeSi is reduced at low temperatures over a wide energy range of ∼ 50 meV below the Fermi level (EF ), which is the energy scale observed by the magnetic, transport and optical measurements. The reduced DOS is completely recovered with increasing temperature but only partly, i.e., predominantly near EF , with Co substitution, again consistent with the transport properties. 7.1 Introduction Among various transition-metal compounds, FeSi shows unique magnetic and transport properties which are sometimes discussed in connection with the characteristics of narrow-gap 4f-electron systems or Kondo insulators [7.1]. At low temperatures FeSi is a nonmagnetic semiconductor. With increasing temperature the magnetic susceptibility rises exponentially to reach a broad maximum at ∼ 500 K and follows a Curie-Weiss law at higher temperatures [7.2]. The electrical resistivity falls more than three orders of magnitude with increasing temperature up to ∼ 300 K [7.3] but rises slowly above ∼ 300 K like a metal. In recent years, the temperature-dependent electronic structure of FeSi has been studied extensively by spectroscopic methods [7.4–14]. Schlesinger 97
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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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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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32 Chapter 3. Photoemission Study o
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44 References the Kondo peak positi
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Page 134 and 135: 130 Chapter 9. Conclusion (a) FeSi
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