Tailoring the Normal and Superconducting State Properties of Ternary Scandium Tellurides, Sc6MTe2 (M = Fe, Ru, and Ir) Through Chemical Substitution

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 Sc₆MTe₂ (M = d-electron metal) family has emerged as a unique series of isostructural compounds exhibiting superconductivity across a range of 3d, 4d, and 5d 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 Sc₆FeTe₂, 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 Sc₆MTe₂ compounds. These results classify the Sc₆MTe₂ 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.