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

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114 Chapter 8. Temperature and Al-Substitution Dependence of the ... ρ (m Ω cm) 2.0 1.5 1.0 0.5 0 x = 0.02 x = 0.05 x = 0.10 50 x = 0.30 100 x = 0.00 150 T (K) FeSi 1-x Al x 200 250 300 Figure 8.2: Electrical resistivities of FeSi1−xAlx polycrystals [8.8]. of Fe1−xCoxSi, is (i) the extended measurement temperature range down to 7 K, (ii) the improved pressure in the spectrometer, and (iii) the higher energy resolution. The sample surface was scraped in the ultrahigh vacuum. The base pressure was in the 10 −11 Torr range and remained in the 10 −10 Torr range even with the He lamp working, which is 10 times better than that of the previous system. We evaporated Au on the measured samples to determine the Fermi level (EF ) and the instrumental resolution. The energy resolution for He I spectra was 14-16 meV. The satellite lines are much weak compared with the He I line for the VG lamp, but before dividing the spectra by the Fermi-Dirac (FD) function we have subtracted the background systematically following the procedure described in Chap. 2 to deal with a slight change in the spectral DOS.
8.3. Results and Discussion 115 8.3 Results and Discussion Intensity (arb. units) FeSi 1-x Al x hν = 40.8 eV 7 K x = 0.00 x = 0.02 x = 0.05 x = 0.10 x = 0.30 -10 -8 -6 -4 -2 0 Energy relative to E F (eV) Figure 8.3: Photoemission spectra of FeSi1−xAlx taken with He II. A rise below ∼− 7 eV in the x = 0.02 spectrum might be due to signal from a Cu plate on which the sample is mounted since the size of the x = 0.02 sample was comparable to the spot size of the He lamp. Figure 8.3 shows He II spectra of FeSi1−xAlx in a wide energy range1 . The valence band of FeSi1−xAlx, including that of FeSi0.70Al0.30, is almost identical with that of FeSi. Substitution dependence appears in the high-resolution He I spectra shown in Fig. 8.4. The spectra have been normalized to the intensity below − 0.4 eV. We have subtracted 1 In the case of Fe1−xCoxSi, He II (hν = 40.8 eV) spectra agreed with He I (hν = 21.2 eV) spectra. He I spectra below ∼−8 eV, where the kinetic energy of emitted photoelectrons is rather low, were not perfectly reproducible using the Omicron analyzer and thus we used the He II line to observe the entire valence band.
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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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44 References the Kondo peak positi
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46 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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Page 100 and 101: 96 References [6.11] M. J. Rozenber
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Page 134 and 135: 130 Chapter 9. Conclusion (a) FeSi
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