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

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7.3. Results and Discussion 101<br />

light source we used the He I resonance line (hν = 21.2 eV). The samples were repeatedly<br />

scraped in an ultra-high vacuum with a diamond file to obtain fresh surfaces. The<br />

base pressure <strong>of</strong> the spectrometer was in the 10−11 Torr range. The Fermi edge <strong>of</strong> Au<br />

film evaporated on the sample surface after each series <strong>of</strong> measurements was used to<br />

determine EF and the instrumental resolution. The resolution thus determined was ∼<br />

20 meV.<br />

7.3 Results and Discussion<br />

Intensity<br />

FeSi<br />

297 K<br />

225 K<br />

150 K<br />

75 K<br />

18 K<br />

Fe 0.95Co 0.05Si<br />

Fe 0.90Co 0.10Si<br />

18 K<br />

18 K<br />

hν = 21.2 eV<br />

-10 -8 -6 -4 -2 0<br />

Energy relative to E F (eV)<br />

Figure 7.3: Entire valence-band photoemission spectra <strong>of</strong> Fe1−xCoxSi taken with hν =<br />

21.2 eV.<br />

Figure 7.3 shows the entire valence band <strong>of</strong> Fe1−xCoxSi. As already reported [7.6,<br />

7], the temperature dependence <strong>of</strong> the photoemission spectra <strong>of</strong> FeSi in such a wide<br />

energy scale is negligible. Also, Fig. 7.3 shows that the spectra do not change for

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