First-principles calculation of electron-phonon coupling in doped KTaO3.

Motivated by the recent experimental discovery of strongly surface-plane-dependent superconductivity at surfaces of KTaO single crystals, we calculate the electron-phonon coupling strength, , of doped KTaO along the reciprocal-space high-symmetry directions. Using the Wannier-function approach implemented in the EPW package, we calculate across the experimentally covered doping range and compare its mode-resolved distribution along the [001], [110] and [111] reciprocal-space directions. We find that the electron-phonon coupling is strongest in the optical modes around the Γ point, with some distribution to higher values in the [001] direction.

Interplay between ferroelectricity and metallicity in BaTiO.

We explore the interplay between ferroelectricity and metallicity, which are generally considered to be contra-indicated properties, in the prototypical ferroelectric barium titanate, BaTiO. Using first-principles density functional theory, we calculate the effects of electron and hole doping, first by introducing a hypothetical background charge, and second through the introduction of explicit impurities (La, Nb and V for electron doping, and K, Al and Sc for hole doping). We find that, apart from a surprising increase in polarization at small hole concentrations, both charge-carrier types decrease the tendency towards ferroelectricity, with the strength of the polarization suppression, which is different for electrons and holes, determined by the detailed structure of the conduction and valence bands.