Superconductivity near the Mott-Ioffe-Regel limit in the high-entropy alloy superconductor (ScZrNb)1−x(RhPd)x with a CsCl-type lattice

Abstract

Theoretical analysis of the electronic structure of the high-entropy-type superconductor (ScZrNb)1−x(RhPd)x, x∈(0.35,0.45) is presented. The studied material is a partially ordered CsCl-type structure, with two sublattices, randomly occupied by Sc, Zr, Nb (first sublattice) and Nb, Rh, and Pd (second sublattice). Calculations were done using the Korringa-Kohn-Rostoker method with the coherent potential approximation (KKR-CPA) and take into account the substitutional disorder. Our total energy calculations confirm the preference for the partially ordered structure over the fully random bcc-type one. Electronic densities of states N(E), dispersion relations, and McMillan-Hopfield parameters η (electronic contribution to electron-phonon coupling) are studied as a function of composition. The computed increasing trends in N(EF) and η with x are opposite to what we expected based on the experimental results, where the decrease in the critical temperature with increasing x was found. Very strong electron scattering due to disorder is observed, as the electronic dispersion relations are strongly smeared. As a result, the computed electronic lifetimes τ are very short, leading to a small mean free path of electrons of the order of interatomic distance, which puts (ScZrNb)1−x(RhPd)x near the Mott-Ioffe-Regel limit. The trend in τ(x) is similar to the trend observed experimentally in Tc(x), suggesting that disorder may be the factor that influences Tc in this series of alloys.

Source-reported materials — not catalogue approval

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