Tailoring the Normal and Superconducting State Properties of Ternary Scandium Tellurides, Sc₆<i>M</i>Te₂ (<i>M</i> = Fe, Ru, and Ir) Through Chemical Substitution

Abstract The pursuit of a unifying theory for non‐BCS superconductivity has faced significant challenges. One approach to overcome such challenges is to perform systematic investigations into superconductors containing d ‐electron metals in order to elucidate their underlying mechanisms. Recently, the Sc 6 M Te 2 ( M = d ‐electron metal) family has emerged as a unique series of isostructural compounds exhibiting superconductivity across a range of 3 d , 4 d , and 5 d electron systems. In this study, muon spin rotation, neutron diffraction, and magnetization techniques are employed to probe the normal and superconducting states at a microscopic level. These findings reveal extremely dilute superfluid densities that correlate with the critical temperature ( T c ). Additionally, high‐temperature normal‐state transitions that are inversely correlated with T c are identified. Notably, in Sc 6 FeTe 2 , the superconducting pairing symmetry is most likely characterized by two nodeless gaps, one of which closes as electron correlations diminish in the Ru and Ir Sc 6 M Te 2 compounds. These results classify the Sc 6 M Te 2 compounds ( M = Fe, Ru, Ir) as unconventional bulk superconductors, where the normal‐state transitions and superconducting properties are governed by the interplay between electron correlations and spin‐orbit coupling of the d ‐electron metal.