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

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106 Chapter 7. Temperature and Co-Substitution Dependence of the ... DOS at 0 meV DOS at -30 meV σ (arb.units) 1.00 0.95 0.90 0.85 0.80 1.00 0.95 0.90 0.85 0.80 0.16 0.12 0.08 0.04 0.00 0 Fe 1-x Co x Si 50 100 150 200 Temperature (K) x = 0.10 x = 0.05 x = 0.00 x = 0.10 x = 0.05 x = 0.00 x = 0.10 x = 0.05 x = 0.00 Figure 7.7: Top and middle panels: temperature-dependent spectral DOS at EF and 30 meV below it as deduced from Fig. 7.6. Bottom: electrical conductivity of Fe1−xCoxSi [7.19]. 3d bands), leading to a modulation of the conduction-band DOS and a gap sandwiched by high DOS2 . Recalling that the observed spectra mainly come from transition-metal 3d states [7.22], Co substitution for Fe necessarily leads to changes in the broad peak corresponding to the appearance of Co 3d states even if the physical properties are not much influenced by the substitution3 . Photoemission studies on FeAlxSi1−x and FeSi1−xPx, in which the Fe atoms are not substituted, would give clearer information on the relationship between the collapse of the insulating behavior and the change in the broad peak. 2 In Chap. 4 we have presented the recovery of DOS at EF accompanied by the shift of the Kondo peak position away from EF in Yb1−xLuxB12 3 Son et al. measured photoemission spectra of Fe0.5Co0.5Si and found the peak at ∼−0.7 eV [7.23]. 250 300
7.4. Summary 107 7.4 Summary To conclude, we have measured photoemission spectra of Fe1−xCoxSi and discussed their temperature and x-dependences in comparison with the optical conductivity and the dc conductivity. At low temperatures, the spectral DOS of FeSi show a pseudogap of ∼ 50 meV width, almost equal to the gap size observed in the optical measurements. The pseudogap disappears above ∼ 200 K, consistent with the temperature dependence of the optical conductivity. Co substitution affects low-temperature and low-energy electronic structure of FeSi and recovers the DOS in the vicinity of EF , in parallel with the changes in the dc conductivity.
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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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Page 60 and 61: 56 Chapter 4. Evolution of Electron
Page 63 and 64: References [4.1] G. Aeppli and Z. F
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Page 100 and 101: 96 References [6.11] M. J. Rozenber
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Page 104 and 105: 100 Chapter 7. Temperature and Co-S
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Page 115 and 116: Chapter 8 Temperature and Al-Substi
Page 117 and 118: 8.2. Experimental 113 and Fisk [8.2
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Page 130 and 131: 126 References [8.14] T. Tonogai, A
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Page 134 and 135: 130 Chapter 9. Conclusion (a) FeSi
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