Electronic structures of double perovskites Sr₂(Fe_1-zMn_z)MoO₆: Doping-dependent optical studies

We investigated the optical conductivity spectra σ(ω) of double perovskites Sr₂(Fe_1-zMn_z)MoO₆, 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 Sr₂FeMoO₆ and Sr₂MnMoO₆ near the Fermi level are presented, which turn out to agree with the recent LSDA+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 Sr₂MnMoO₆, and finally developed into a Drude peak in Sr₂FeMoO₆. 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.