We have investigated the electronic structure of Sr 2 FeMoO 6 by photoemission spectroscopy and bandstructure calculations within the local-density approximationϩU (LDAϩU) scheme. In valence-band photoemission spectra, a distinct double-peak feature has been observed near the Fermi level (E F ). A photon-energy dependence of the spectra and the LDAϩU band-structure calculation have revealed that the first peak crossing E F consists of the ͑FeϩMo͒ t 2g↓ states and the second peak well below E F is dominated by the Fe e g↑ states. This clearly shows that only the down-spin states contribute to the E F intensity, thus the half-metallic density of states ͑DOS͒ is realized. We point out that the observed half-metallic DOS can be attributed to the strong Hund's rule energy stabilization due to the high-spin 3d 5 configuration at the Fe site.
We have performed a photoemission and inverse photoemission spectroscopic study of a narrow-gap semiconductor FeGa 3 , in order to characterize the occupied and unoccupied electronic states. The energy-gap size was found to be ∼0.4 eV, and the valence-band maximum (VBM) was located around the A point of the Brillouin zone. We observed a dispersive Ga 4sp derived band near the Fermi level (E F), and Fe 3d narrow bands located at −0.5 and −1.1 eV away from E F. In contrast to the case of FeSi, there was no temperature-dependent peak enhancement at the VBM on cooling. The observed density of states and band dispersions were reasonably reproduced by the LDA + U calculation with the on-site effective Coulomb interaction U eff ∼ 3 eV to the Fe 3d states. Present results indicate that, in spite of sizable U eff /W ∼ 0.6 (W : band width), electron correlation effects are not significant in FeGa 3 compared with FeSi since the VBM consists of the dispersive band with the reduced Fe 3d contribution, and the energy gap is large.
We have investigated the electronic structure of electron-doped Sr2−xLaxFeMoO6 (x=0.0 and 0.2) by photoemission spectroscopy and band-structure calculations within the local-density approximation+U (LDA+U ) scheme. A characteristic double-peak feature near the Fermi level (EF) has been observed in the valence-band photoemission spectra of both x=0.0 and 0.2 samples. A photon-energy dependence of the spectra in the Mo 4d Cooper minimum region compared with the band-structure calculations has shown that the first peak crossing EF consists of the (Fe+Mo) t 2g↓ states (feature A) and the second peak well below EF is dominated by the Fe e g↑ states (feature B). Upon La substitution, the feature A moves away from EF by ∼50 meV which is smaller than the prediction of our band theory, 112 meV. In addition, an intensity enhancement of both A and B has been observed, although B is not crossing EF. Those two facts are apparently incompatible with the simple rigid-band shift due to electron doping. We point out that such phenomena can be understood in terms of the strong Hund's rule energy stabilization in the 3d 5 configuration at the Fe sites in this compound. From an observed band-narrowing, we have also deduced a mass enhancement of ∼2.5 with respect to the band theory, in good agreement with a specific heat measurement.
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