  We report the discovery of bulk superconductivity in Sc6MTe2 with seven kinds
of transition-metal elements M. The critical temperatures for M = 3d elements
are higher than those for 4d and 5d elements and increase in the order of M =
Ni, Co, and Fe with the highest Tc of 4.7 K in Sc6FeTe2. First principles
calculations indicate the presence of significant contribution of Fe 3d
orbitals at the Fermi energy, which most likely enhance the Tc of Sc6FeTe2. The
upper critical field for M = Os is considerably enhanced by the strong
spin-orbit coupling. These results show Sc6MTe2 to constitute a unique family
of d-electron superconductors, in which d electrons of 3d and 5d M atoms
strongly influence the superconducting properties.
