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

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44 References the Kondo peak position εf reported for YbAgCu4 may be due to the smallness of εf compared to the instrumental resolution. [3.13] T. Saitoh, A. Sekiyama, T. Mizokawa, A. Fujimori, K. Ito, H. Nakamura, and M. Shiga, Solid State Commun. 95, 307 (1995). [3.14] J.-J. Yeh and I. Lindau, At. Data Nucl. Data Tables 32, 1 (1985). [3.15] F. Gerken, J. Phys. F 13, 703 (1983). [3.16] G. D. Mahan, Phys. Rev. B 11, 4814 (1975). [3.17] F. Iga, Doctor Thesis, Tohoku University, 1988. [3.18] K. N. R. Taylor and M. I. Darby, in Physics of Rare Earth Solids (Chapman and Hall, 1972) p. 8. [3.19] N. E. Bickers, D. L. Cox, and J. W. Wilkins, Phys. Rev. Lett. 54, 230 (1985). [3.20] A. Yanase and H. Harima, Prog. Theor. Phys. Suppl. 108, 19 (1992). [3.21] R. W. Godby, in Unoccupied Electronic States, edited by J. C. Fuggle and J. E. Inglesfield (Springer-Verlag, 1992) p. 51. [3.22] K. Tsutsui, Y. Ohta, R. Eder, S. Maekawa, E. Dagotto, and J. Riera, Phys. Rev. Lett. 76, 279 (1996); T. Saso and M. Itoh, Phys. Rev. B 53, 687 (1996). [3.23] M. M. Steiner, R. C. Albers, and L. J. Sham, Phys. Rev. Lett. 72, 2923 (1994). [3.24] A. Khurana, Phys. Rev. B 40, 4316 (1989). [3.25] C. M. Varma, P. B. Littlewood, S. Schmitt-Rink, E. Abrahams, and A. E. Ruckenstein, Phys. Rev. Lett. 63, 1996 (1989). [3.26] Y. Kuramoto, Z. Phys. B 53 37 (1983); H. Kojima, Y. Kuramoto, and M. Tachiki, Z. Phys. B 54 293 (1984); Y. Kuramoto and H. Kojima, Z. Phys. B 57 95 (1984). [3.27] R. Takayama and O. Sakai, unpublished.
Chapter 4 Evolution of Electronic States in the Kondo Alloy System Yb1−xLuxB12 We have studied the effect of Lu-substitution on the Kondo insulator YbB12 by highresolution photoemission. Comparison of the spectra of YbB12, Yb0.5Lu0.5B12 and LuB12 reveals that the density of states (DOS) of the B sp-derived conduction band near the Fermi level is reduced in YbB12 over a rather wide (∼ 40 meV) energy region. Lu-substitution (i) recovers the reduced B sp DOS, (ii) shifts the Yb 4f-derived Kondo peak towards higher binding energy and (iii) decreases the Yb valence. These results are consistently analyzed using the Anderson-impurity model, and imply interaction between the Yb 4f ions mediated by the Yb 4f-B sp hybridization in YbB12. 4.1 Introduction Kondo insulators have attracted many researchers’ attention due to their unique ground states and unusual low-energy excited properties [4.1–3]. In a preceding work [4.4], we have pursued this issue from the photoemission spectroscopic point of view for YbB12, which is the only Yb-based Kondo insulator.[4.5, 6] We have found that the observed position of the Kondo peak agrees well with the Kondo temperature (TK) deduced from the magnetic susceptibility in the framework of the single-impurity model. The highly asymmetric Kondo peak has been explained by a strongly energy dependent self-energy correction to the one-electron band structure [4.4, 7–9]. Since that work, some questions have remained unanswered. Firstly, there has not been a clear indication of gap opening at EF in the spectra of YbB12 [4.10]. Secondly, the effects of hybridization between the 45
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Page 4 and 5: ii CONTENTS 5.2 Experimental . . .
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Page 27 and 28: 2.2. Experimental 23 DOS Intensity
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96 References [6.11] M. J. Rozenber
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98 Chapter 7. Temperature and Co-Su
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100 Chapter 7. Temperature and Co-S
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Chapter 8 Temperature and Al-Substi
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8.3. Results and Discussion 115 8.3
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8.3. Results and Discussion 117 Int
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8.3. Results and Discussion 119 dep
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8.3. Results and Discussion 121 σ
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8.4. Summary 123 temperature magnet
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126 References [8.14] T. Tonogai, A
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