Cocktail effect on superconductivity in hexagonal high-entropy alloys

TL;DR

This study investigates how compositional complexity in hexagonal high-entropy alloys enhances superconductivity, revealing that phonon softening and electron-phonon interactions play key roles in increasing the transition temperature.

Contribution

It demonstrates the cocktail effect's impact on superconductivity in hexagonal HEAs and links Tc enhancement to phonon softening and electron-phonon coupling.

Findings

Tc is enhanced by up to an order of magnitude compared to elemental averages.

Superconducting properties correlate with phonon softening and electron-phonon coupling.

Tc scales with inverse molecular weight and decreases with higher mixing entropy.

Abstract

We report the study of the cocktail effect on superconductivity in high-entropy alloys (HEAs),using hexagonal close-packed HEAs as a prototype system. Compared with the compositional averages of the constituent elements, the superconducting transition temperature Tc is enhanced by from a factor of about 2 to over one order of magnitude. This Tc enhancement correlates with the reduction in the Debye temperature, underlining the importance of phonon softening in triggering the cocktail effect. Furthermore, we show that the Tc in these HEAs is governed by the average phonon frequency and electron-phonon coupling strength, the latter of which scales linearly with the inverse HEA molecular weight and is progressively weakened with increasing mixing entropy. Our study paves the way toward quantitative understanding of the superconductivity in HEAs.