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

More documents

Recommendations

Info

116 Chapter 8. Temperature and Al-Substitution Dependence of the ... Intensity (arb. units) FeSi 1-x Al x hν = 21.2 eV 7 K x = 0.00 x = 0.02 x = 0.05 x = 0.10 x = 0.30 × 5 Difference from x = 0.00 -0.4 -0.2 0 Energy relative to E F (eV) (a) (b) Intensity (arb. units) FeSi1-xAlx hν = 21.2 eV 295 K x = 0.00 x = 0.02 x = 0.05 x = 0.10 x = 0.30 × 5 Difference from x = 0.00 -0.4 -0.2 0 Energy relative to E F (eV) Figure 8.4: Photoemission spectra of FeSi1−xAlx taken at 7 K (a) and at 295 K (b). Difference spectra between FeSi1−xAlx and FeSi are shown in the lower panels. the spectra of FeSi from those of FeSi1−xAlx as shown in the lower panels of Fig. 8.4 (a) and (b). The change in the spectra with Al substitution is 4 % at 7 K and reaches 7 % at 295 K. Also, the substitution dependence appears in wider energy region at 295 K. Spectral weight in the whole energy region between EF and − 300 meV is reduced with substitution at 295 K. Such a decrease with substitution is also present at 7 K, but the spectral DOS within 30 meV of EF increases as shown in Fig. 8.5 on an enlarged energy scale. Although the substitution-induced change in the spectra extends up to ∼−0.3 eV, the position of the broad peak at ∼−0.3 eV does not show a substantial change. Temperature-dependent spectral DOS of each sample is shown in Fig. 8.6, where the photoemission spectra have been divided by the FD function convoluted with a Gaussian corresponding to the instrumental resolution. The spectra have also been normalized below − 0.4 eV. The temperature-dependent depression of the spectral DOS disappears in the x = 0.30 spectra.
8.3. Results and Discussion 117 Intensity (arb. units) Difference (7 K) 0.02 - 0.00 0.05 - 0.00 0.10 - 0.00 0.30 - 0.00 -0.15 -0.10 -0.05 0 Energy relative to E F (eV) Figure 8.5: Difference spectra at 7 K plotted on an enlarged energy scale. Substitution dependence of the depression at various energies are plotted in Fig. 8.7. The depression in going from x = 0.30 to x = 0.10 is almost energy independent, indicating that the pseudogap is deepened uniformly. In going from x = 0.10 to 0.05 and 0.02, the depression within 50 meV of EF increases while that below − 100 meV decreases. This means that the pseudogap of larger than ∼ 50 meV opens between x = 0.10 and 0.05. Note that the negative slope in the T -ρ curve appears at low temperatures for x ∼< 0.10 [8.8]. In going from x = 0.02 to 0.00 the curves show an energy-independent shift again2 . Based on the hybridization gap model for the Kondo insulators, hybridization between the conduction band and the localized band develops a gap sandwiched by a high DOS. Recent tunneling spectroscopy of FeSi [8.12] reveals the quasiparticle DOS peaks evolves at 50-70 mV on the both side of a gap on cooling. On the other hand, no growth 2 This shift corresponds to a uniform depression of the DOS for x = 0.00 at 7 K, as is visible in Fig. 8.6 (a) and (b) while such a depression is absent in the raw spectra. Probably the background slope at 7 K was different from those at other temperatures for x = 0.00.
Page 1:
Thesis High-Resolution Photoemissio
Page 4 and 5:
ii CONTENTS 5.2 Experimental . . .
Page 6 and 7:
2 Chapter 1. Introduction Figure 1.
Page 8 and 9:
4 Chapter 1. Introduction Figure 1.
Page 10 and 11:
6 Chapter 1. Introduction peaks, wh
Page 12 and 13:
8 Chapter 1. Introduction only the
Page 14 and 15:
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 38 and 39:
Page 40 and 41:
Page 42 and 43:
Page 44 and 45:
Page 46 and 47:
Page 48 and 49:
44 References the Kondo peak positi
Page 50 and 51:
46 Chapter 4. Evolution of Electron
Page 52 and 53:
Page 54 and 55:
Page 56 and 57:
Page 58 and 59:
Page 60 and 61:
Page 63 and 64:
References [4.1] G. Aeppli and Z. F
Page 65:
References 61 [4.25] P. Weibel,M. G
Page 68 and 69:
64 Chapter 5. Temperature Dependenc
Page 70 and 71: 66 Chapter 5. Temperature Dependenc
Page 78 and 79: 74 References [5.10] N. Shimizu, F.
Page 81 and 82: Chapter 6 Substitution and Temperat
Page 83 and 84: 6.1. Introduction 79 Figure 6.2: Ma
Page 85 and 86: 6.3. Results and Discussion 81 6.3
Page 87 and 88: 6.3. Results and Discussion 83 DOS
Page 89 and 90: 6.3. Results and Discussion 85 dist
Page 91 and 92: 6.3. Results and Discussion 87 Apar
Page 93 and 94: 6.3. Results and Discussion 89 of E
Page 95 and 96: 6.3. Results and Discussion 91 the
Page 97: 6.4. Summary 93 and consistent anal
Page 100 and 101: 96 References [6.11] M. J. Rozenber
Page 102 and 103: 98 Chapter 7. Temperature and Co-Su
Page 104 and 105: 100 Chapter 7. Temperature and Co-S
Page 113 and 114: References [7.1] G. Aeppli and Z. F
Page 115 and 116: Chapter 8 Temperature and Al-Substi
Page 117 and 118: 8.2. Experimental 113 and Fisk [8.2
Page 119: 8.3. Results and Discussion 115 8.3
Page 123 and 124: 8.3. Results and Discussion 119 dep
Page 125 and 126: 8.3. Results and Discussion 121 σ
Page 127: 8.4. Summary 123 temperature magnet
Page 130 and 131: 126 References [8.14] T. Tonogai, A
Page 132 and 133: 128 Chapter 9. Conclusion has shown
Page 134 and 135: 130 Chapter 9. Conclusion (a) FeSi
Page 136: 132 Chapter 9. Conclusion developed
show all

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

Create successful ePaper yourself

Delete template?

Save as template?