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

Tobias Esswein1*, Nicola A. Spaldin1*

1 Materials Theory, Department of Materials, ETH Zürich, Wolfgang-Pauli-Strasse 27, 8093 Zürich, Switzerland

* Corresponding authors emails: tobias.esswein@mat.ethz.ch, nicola.spaldin@mat.ethz.ch
DOI10.24435/materialscloud:3t-k3 [version v3]

Publication date: Aug 28, 2023

How to cite this record

Tobias Esswein, Nicola A. Spaldin, First-principles calculation of electron-phonon coupling in doped KTaO₃, Materials Cloud Archive 2023.132 (2023), https://doi.org/10.24435/materialscloud:3t-k3


Motivated by the recent experimental discovery of strongly surface-plane-dependent superconductivity at surfaces of KTaO3 single crystals, we calculate the electron-phonon coupling strength, λ, of doped KTaO3 along the reciprocal-space high-symmetry directions. Using the Wannier-function approach implemented in the EPW package, we calculate λ 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 k values in the [001] direction. The electron-phonon coupling strength as a function of doping has a dome-like shape in all three directions and its integrated total is largest in the [001] direction and smallest in the [111] direction, in contrast to the experimentally measured trends in critical temperatures. This disagreement points to a non-BCS character of the superconductivity. Instead, the strong localization of λ in the soft optical modes around Γ suggests an importance of ferroelectric soft-mode fluctuations, which is supported by our findings that the mode-resolved λ values are strongly enhanced in polar structures. The inclusion of spin-orbit coupling has negligible influence on our calculated mode-resolved λ values.

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electron-phonon coupling KTaO3 ab initio