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

118 Chapter 8. Temperature and Al-Substitution Dependence of the ...
DOS
(a) (b)
x = 0.00
x = 0.02
x = 0.05
x = 0.10
x = 0.30
FeSi 1-x Al x
295 K
7 K
-400 -200 0
Energy relative to E F (meV)
DOS
x = 0.00
x = 0.02
x = 0.05
x = 0.10
x = 0.30
FeSi 1-x Al x
295 K
7 K
-150 -100 -50 0 50
Energy relative to E F (meV)
Figure 8.6: Temperature-dependent spectral DOS of FeSi1−xAlx (a). For each sample,
T = 7 K (thick curves), 75 K, 150 K, 225 K, and 295 K from bottom. The vicinity of
EF is enlarged in (b).
corresponding to such quasiparticle DOS is observed in the photoemission spectra of
FeSi on cooling and the DOS is monotonously decreased with lowering temperature3 .
However, a broad peak develops around EF with decreasing Al concentration as
shown in Fig. 8.4 (a) and (b). Here we have subtracted the x = 0.30 DOS at 7 K
from the other DOS and have presented the temperature dependence of the difference
DOS of each sample [Fig. 8.8 (a)] and the substitution dependence of the difference
DOS at each temperature [Fig. 8.8 (b)]. Temperature dependence appears mainly from
EF to ∼−100 meV in the x = 0.00, 0.02, 0.05, and 0.10 spectra. Especially, the
depression of FeSi at low temperature in the vicinity of EF , which is recovered with a
3 Saitoh et al. [8.13] compared the photoemission spectra of FeSi with the DOS from the bandstructure
calculation [8.3] corrected with a model self-energy and pointed out that due to a strong
band narrowing the peak of the quasiparticle DOS is located just ∼ 10 meV below EF although the
photoemission spectrum showed a maximum around ∼−0.3 eV.