Unusual electron-doping effects inSr2−xLaxFeMoO6observed by photoemission spectroscopy

Abstract

We have investigated the electronic structure of electron-doped ${\mathrm{Sr}}_{2\ensuremath{-}x}{\mathrm{La}}_{x}\mathrm{Fe}\mathrm{Mo}{\mathrm{O}}_{6}$ ($x=0.0$ and 0.2) by photoemission spectroscopy and band-structure calculations within the local density $\text{approximation}+U$ scheme. A characteristic double-peak feature near the Fermi level $({E}_{\mathrm{F}})$ 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 $\mathrm{Mo}\phantom{\rule{0.2em}{0ex}}4d$ Cooper minimum region compared with the band-structure calculations has shown that the first peak crossing ${E}_{\mathrm{F}}$ consists of the $(\mathrm{Fe}+\mathrm{Mo})$ ${t}_{2g\ensuremath{\downarrow}}$ states (feature A) and the second peak well below ${E}_{\mathrm{F}}$ is dominated by the $\mathrm{Fe}\phantom{\rule{0.2em}{0ex}}{e}_{g\ensuremath{\uparrow}}$ states (feature B). Upon La substitution, the feature A moves away from ${E}_{\mathrm{F}}$ by $\ensuremath{\sim}50\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$, which is smaller than the prediction of our band theory, $112\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$. In addition, an intensity enhancement of both A and B has been observed, although B does not cross ${E}_{\mathrm{F}}$. 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 $3{d}^{5}$ configuration at the Fe sites in this compound. From an observed band-narrowing, we have also deduced a mass enhancement of $\ensuremath{\sim}2.5$ with respect to the band theory, in good agreement with a specific heat measurement.