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

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