Superconductivity in Ternary Scandium Telluride Sc₆<i>M</i>Te₂ with 3<i>d</i>, 4<i>d</i>, and 5<i>d</i> Transition Metals

Abstract

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.Superconductivity in d-electron systems has been one of the central issues in condensed matter physics.There are many outstanding superconductors, such as cuprates 1 , iron arsenides and selenides 2,3 , spinel LiTi2O4 4 , layered perovskite Sr2RuO4 5 , hydrate NaxCoO2•nH2O 6 , -pyrochlore KOs2O6 7 , and kagome CsV3Sb5 8 .The d electrons of the transition metals play a major role in determining their electrical properties and the cooperation between various features of d electrons, such as strong electron correlation, strong spin-orbit coupling, and strong spin and orbital fluctuations, results in the emergence of unique unconventional superconductivities.However, such d-electron superconductivities appear only in materials with specific combinations of transition metal elements and crystal structure.For example, almost all transition metal compounds that are isostructural to the above superconductors but contain other transition metal elements do not exhibit superconductivity.A recently discovered layered nickelate superconductor, a Ni analogue of high-Tc cuprates, is a rare counter example 9 .This nature of d-electron superconductors prevents a complete understanding of their features based on systematic experimental studies.Here, we report the ternary telluride series Sc6MTe2 as a unique family of d-electron superconductors incorporating 3d, 4d, and 5d electron systems.Sc6MTe2 compounds with M = Mn, Fe, Co, Ni, Ru, Rh, Os, and Ir have been synthesized and reported to crystallize in the hexagonal Zr6CoAl2-type structure with space group P-62m without inversion symmetry, but their physical properties have not been reported thus far 10,11 .A characteristic point of this crystal

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