Superconductivity in Al-based high-entropy alloys TiHfNbTaAl and TaNbHfZrAl

Abstract Since the first report of a high-entropy alloy (HEA) superconductor in 2014, HEAs have continued to captivate the interest of superconducting researchers. Owing to the significant degree of disorder inherent in these systems, they serve as exemplary models for examining the properties of materials that exist in states intermediate between crystalline and amorphous structures. Here we present the superconductivity properties and crystal structure of TaNbHfZrAl and TiHfNbTaAl HEAs, which both have the valence electron count (VEC) of 4.2 and body-centered cubic (BCC) structure. Through resistivity, magnetic, and specific heat measurements, we prove that both samples are the bulk type-II superconductors with a critical temperature T c of 5.5 K for TaNbHfZrAl and T c of 3.2 K for TiHfNbTaAl. The T c of HEA superconductors is influenced by the VEC and the element composition. And the incorporation of Al in high disorder HEA superconductors causes a more crystallinelike T c dependence. We also found that the ΔC el /γ T c mid (2.31) and 2Δ 0 / K B T c (4.48) of the TaNbHfZrAl sample are close to the known strongly coupled systems, suggesting that it is a strongly coupled superconductor. The TaNbHfZrAl HEA system serves as a novel material platform for exploring strongly coupled phenomena.