Many-body large polaron optical conductivity in SrTi$_{1-x}$Nb$_{x}$O$_{3}$*

Recent experimental data on the optical conductivity of niobium doped SrTiO$_{3}$ are interpreted in terms of a gas of large polarons. The theoretical approach takes into account many-body effects, the electron-phonon interaction with multiple LO-phonon branches, and the degeneracy and the anisotropy of the Ti t$_{2g}$ conduction band. The many-body large-polaron model based on the Fr\"{o}hlich interaction provides a fair agreement between the theoretical large-polaron optical conductivity band and the experimental mid-infrared optical conductivity band without any adjustment of material parameters. The large-polaron model gives then a convincing interpretation of the experimentally observed optical conductivity spectra of SrTi$_{1-x}$Nb$_{x}$O$_{3}$.