Superconductivity in SrTiO${}_3$: dielectric function method for non-parabolic bands

The dielectric function method for superconductivity has been applied to SrTiO${}_3$ accounting for the non-parabolic dispersion of charge carriers in the conduction band and for the dispersion of optical phonons based on density functional theory calculations. The obtained critical temperatures of the superconducting phase transition in SrTiO${}_3$ are in agreement with experiments in the density range $n\sim 5\times {10}^{18}$ to $5\times {10}^{20}$ cm${}^{-3}$. The dielectric function method predicts also the sign of the anomalous isotope effect in strontium titanate, in line with recent observations.