Tailoring the normal and superconducting state properties of ternary scandium tellurides, Sc${}_{6}M$Te${}_2$ ($M=$ 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 \textit{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 $3d$, $4d$, and $5d$ electron systems. In this study, we employ muon spin rotation, neutron diffraction, and magnetisation techniques to probe the normal and superconducting states at a microscopic level. Our findings reveal extremely dilute superfluid densities that correlate with the critical temperature ($T_{\mathrm{c}}$). Additionally, we identify high-temperature normal-state transitions that are inversely correlated with $T_{\mathrm{c}}$. Notably, in Sc${}_6$FeTe${}_2$, the superconducting pairing symmetry is most likely characterised 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.

11 pages, 10 figures