Electronic structures of double perovskitesSr2(Fe1−zMnz)MoO6:Doping-dependent optical studies

Abstract

We investigated the optical conductivity spectra $\ensuremath{\sigma}(\ensuremath{\omega})$ of double perovskites ${\mathrm{Sr}}_{2}({\mathrm{Fe}}_{1\ensuremath{-}z}{\mathrm{Mn}}_{z}){\mathrm{MoO}}_{6},$ which show filling controlled metal--insulator transition. Based on systematic analyses of optical conductivity and O $1s$ x-ray absorption spectroscopy, the electronic structures of both ${\mathrm{Sr}}_{2}{\mathrm{FeMoO}}_{6}$ and ${\mathrm{Sr}}_{2}{\mathrm{MnMoO}}_{6}$ near the Fermi level are presented, which turn out to agree with the recent $\mathrm{LSDA}+\mathrm{U}$ calculation results [H. Wu, Phys. Rev. B 64, 125126 (2001)]. With the Mo carrier doping (with z decreasing), the in-gap spectral weight is formed, below the gap of ${\mathrm{Sr}}_{2}{\mathrm{MnMoO}}_{6},$ and finally developed into a Drude peak in ${\mathrm{Sr}}_{2}{\mathrm{FeMoO}}_{6}.$ Due to the possible site disorder, finite energy peaks rather than Drude-like peaks were observed for most of the doping ranges $0.2<~z<~0.8.$ With the ferrimagnetic ordering, we observed redistribution of spectral weight over a wide energy region from 0 to 3 eV. The high energy spectral weight was transferred to the low energy region, similar to the manganites. We discussed possible scenarios relevant to the Fe--Mo hybridization.