Angle-resolved photoemission analysis of electronic structures for thermoelectric properties of off-stoichiometric FeVAl alloys

Soda, Kazuo*; Harada, Shota*; Hayashi, Toshimitsu*; Kato, Masahiko*; Ishikawa, Fumihiro*; Yamada, Yu*; Fujimori, Shinichi   ; Saito, Yuji  

The electronic states of Heusler(L21)-type off-stoichiometric FeVAl have been investigated by soft X-ray angle-resolved photoelectron spectroscopy (ARPES) in order to clarify the origin of their large thermoelectric powers, which cannot be explained in terms of the rigid band model. In off-normal and normal ARPES, FeVAl shows a weakly dispersive bulk band around the binding energy of 0.3 eV in the -X direction and an almost dispersion-less one around 0.3 eV in a gap of dispersive bulk bands in the -L direction, which is attributed to the anti-site Fe defect. At the point, the bulk band does not appear to cross the Fermi level , consistent with the rigid band model for the excess Fe content bringing about the increase in the valence electrons, but no band crossing down is found at the X point. The anti-site Fe defect states near might push up the band at the X point and cause the p-type thermoelectric properties, unexpected with the rigid band picture. The change in the electronic structures and thermoelectric properties are discussed on the off-stoichiometry and substitution of the forth element.