Tuning of the electronic screening and electron-phonon coupling in dopedSrTiO3andWO3

The electronic structure and the electronic part of the electron-phonon coupling $\lambda$ is calculated for doped ${\mathrm{SrTiO}}_3$ and ${\mathrm{WO}}_3$ systems in the perovskite structure. Dilute doping is treated by supercells and the virtual crystal approximation. The long-range part of the coupling is found to be weakly screened for low doping, when the material is close to insulating. The low-$q$ part of $\lambda$ becomes large despite the low density of states. This is consistent with the appearance of superconductivity for dilute doping.