Electronic Raman scattering in filling-controlled metals: ${\mathrm{Sr}}_{1\mathrm{-}\mathit{x}}$${\mathrm{La}}_{\mathit{x}}$${\mathrm{TiO}}_3$

Electronic Raman scattering has been investigated for metallic ${\mathrm{Sr}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{La}}_{\mathit{x}}$ ${\mathrm{TiO}}_3$ in which the 3d band filling (x) can be systematically changed from x=0 (a band insulator) to x=1 (a Mott-Hubbard insulator). The symmetry dependence of the scattering intensity can be accounted for in terms of the neutral carrier density fluctuation model. However, a systematic change of the spectral shape with the carrier density (≃x) is observed. All the spectra can be reproduced by a relaxational function with an ω-dependent scattering rate (Γ). The ω dependence of Γ gets stronger with x, which is in accord with the x-dependent enhancement of the effective mass, due to the electron correaltion effect.