Unusual electron-doping effects in Sr2-xLaxFeMoO6 observed by photoemission spectroscopy

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 scheme. A characteristic double-peak feature near the Fermi level (E-F) 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 E-F consists of the (Fe+Mo) t(2g down arrow) states (feature A) and the second peak well below E-F is dominated by the Fe e(g up arrow) states (feature B). Upon La substitution, the feature A moves away from E-F by similar to 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 does not cross E-F. 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 similar to 2.5 with respect to the band theory, in good agreement with a specific heat measurement.