Strong-coupling superconductivity of the Heusler-type compound ScAu2Al: Ab initio studies

Abstract

The ScAu2Al superconducting Heusler-type compound was recently characterized to have the highest critical temperature of Tc=5.12 K and the strongest electron-phonon coupling among the Heusler family. In this work, the electronic structure, phonons, electron-phonon coupling, and superconductivity of ScAu2Al are studied using ab initio calculations. The spin-orbit coupling significantly changes the electronic structure removing the van Hove singularity from the vicinity of the Fermi level. In the phonon spectrum, low-frequency acoustic modes, additionally softened by the spin-orbit interaction, strongly couple with electrons, leading to the electron-phonon coupling constant λ=1.25, a record high among Heuslers. The density functional theory for superconductors is then used to analyze superconducting state in this two-band superconductor. The effect of spin fluctuations (SF) on superconductivity is also analyzed. The calculated critical temperatures of Tc=5.16 K (4.79 K with SF) agree very well with the experiment, confirming the electron-phonon mechanism of superconductivity and showing a weak spin-fluctuation effect. The superconducting gaps formed on two Fermi surface sheets exhibit moderate anisotropy. Their magnitudes confirm the strong coupling regime, as the reduced average values are 2Δb1/kBTc≃4.1 and 2Δb2/kBTc≃4.3. Anisotropy of the gaps and large spread in their values significantly affect the calculated quasiparticle density of states.

Source-reported materials — not catalogue approval

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