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### First-principles calculation of electron-phonon coupling in doped KTaO3
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Tobias Esswein and Nicola A. Spaldin
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https://arxiv.org/abs/2210.14113
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#### Abstract:
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] 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 is largest in the 
[001] direction and weakest in the [111] direction. This is in contrast to the 
experimentally measured critical temperatures, which are highest for the (111) 
plane, pointing to a non-BCS character of the superconductivity. The strong 
localization of λ in the soft optical modes around Γ suggests an importance of 
ferroelectric soft-mode fluctuations.
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All calculations were performed using Quantum Espresso (version 7.0) with 
GBRV pseudopotentials using the PBEsol exchange-correlation functional.
All input files are provided in the archive.