Nodeless superconductivity in the cage-type superconductor Sc 5 Ru 6 Sn 18 with preserved time-reversal symmetry.

We report the single-crystal synthesis and detailed investigations of the cage-type superconductor Sc5Ru6Sn18, using powder x-ray diffraction (XRD), magnetization, specificheat and muon-spin relaxation (mu/SR) measurements. Sc5Ru6Sn18 crystallizes in a tetragonal structure (space group I4(1)/acd) with lattice parameters a = 1.387(3) nm and c = 2.641(5) nm. Both DC and AC magnetization measurements prove the type-II superconductivity in Sc5Ru6Sn18 with T-c approximate to 3.5(1) K, a lower critical field H-c1 (0) = 157(9) Oe and an upper critical field, H-c2 (0) = 26(1) kOe. The zero-field electronic specific-heat data are well fitted using a single-gap BCS model, with Delta(0) = 0.64(1) meV. The Sommerfeld constant gamma varies linearly with the applied magnetic field, indicating s-wave superconductivity in Sc5Ru6Sn18. Specificheat and transverse-field (TF) OR measurements reveal that Sc5Ru6Sn18 is a superconductor with strong electron-phonon coupling, with TF-mu SR also suggesting a single-gap s-wave character of the superconductivity. Furthermore, zero-field mu SR measurements do not detect spontaneous magnetic fields below T-c, hence implying that time-reversal symmetry is preserved in Sc5Ru6Sn18.