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

Chapter 8
Temperature and Al-Substitution
Dependence of the Photoemission
Spectra of FeSi
We have performed temperature-dependent high-resolution photoemission measurements
on FeSi1−xAlx (x = 0.00, 0.02, 0.05, 0.10, and 0.30) and have identified three
different energy regions near the Fermi level (EF ) from the different responses of the
spectral density of states (DOS) to temperature and Al substitution. That is, the dip
in the vicinity (∼ 20 meV) of EF which is sensitive to a small amount of Al substitution
and a small temperature increase, the pseudogap region (∼ 50 meV) whose
depth smoothly depends on Al substitution and temperature, and the shoulder near
the valence-band top (∼ 100 meV), which grows with decreasing Al concentration in
going from x = 0.30 to 0.00. The broad peak at ∼ 400 meV below EF is stable against
both temperature and substitution unlike that in Fe1−xCoxSi, where the peak position
moved for a small amount of Co substitution.
8.1 Introduction
In the preceding photoemission study of FeSi, we have found that Co substitution
recovers the density of states (DOS) in the vicinity of the Fermi level (EF ) and does
not modify the size of the pseudogap of ∼ 50 meV. The broad peak at ∼−0.3 eV
also depends on the substitution and is shifted to higher binding energies with Co
substitution. However, although Co substitution increases the band filling in FeSi, it
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