Increased Superconducting Transition Temperature and Upper Critical Field of a High-Entropy Antimonide Superconductor (RuRhPdIr)1–xPtxSb

High-entropy compounds have garnered significant interest in recent years owing to their exceptional properties and functionalities derived from the cocktail effect, which indicates that the properties of high-entropy compounds will be significantly enhanced compared to the average properties obtained from the individual properties of the constituent elements. Herein, we report an increased superconducting transition temperature (T_c) and upper critical field (H_c2) as a new cocktail effect in the high-entropy antimonide superconductor (RuRhPdIr)_1–xPt_xSb, where x denotes the Pt content. Transport measurements revealed a composition-dependent systematic change from unusual transport properties due to the extremely strong scattering of electrons and phonons for x = 0.2 to a normal metallic state for x = 1 (PtSb). T_c also varied with the Pt content, which could be attributed to the change in the electron–phonon coupling, reaching a maximum of 3.1 K at x = 0.4. This was the highest value among the transition metal mono antimonides. The H_c2 value for x = 0.2 was 7 times higher than that for x = 1, which is likely attributed to the shortening of the coherence length due to chemical disorder. This study demonstrates that extremely strong chemical disorders in high-entropy compounds may be effective in improving their superconducting properties.