Nodeless superconductivity in the cage-type superconductor Sc₅Ru₆Sn₁₈ with preserved time-reversal symmetry

Abstract

We report the single-crystal synthesis and detailed investigations of the cage-type superconductor ScRuSn, using powder x-ray diffraction (XRD), magnetization, specific-heat and muon-spin relaxation (µSR) measurements. ScRuSn crystallizes in a tetragonal structure (space group I4/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 ScRuSn with T ≈ 3.5(1) K, a lower critical field [Formula: see text] = 157(9) Oe and an upper critical field, [Formula: see text] = 26(1) kOe. The zero-field electronic specific-heat data are well fitted using a single-gap BCS model, with [Formula: see text] = 0.64(1) meV. The Sommerfeld constant γ varies linearly with the applied magnetic field, indicating s-wave superconductivity in ScRuSn. Specific-heat and transverse-field (TF) µSR measurements reveal that ScRuSn is a superconductor with strong electron-phonon coupling, with TF-µSR also suggesting a single-gap s-wave character of the superconductivity. Furthermore, zero-field µSR measurements do not detect spontaneous magnetic fields below T , hence implying that time-reversal symmetry is preserved in ScRuSn.

Conventional isotropic s -wave superconductivity with strong electron-phonon coupling in Sc5Rh6Sn18

“…For a sufficiently accurate description of c ph (T ) of Sc 5 Rh 6 Sn 18 in the whole temperature range, it was necessary to include even the T 7 term, i.e., c p = γ tot T + βT 3 + δT 5 + T 7 . The resulting parameters of such a fit in the temperature range 0.35-6.1 K are the Sommerfeld coefficient of the electronic heat capacity γ tot = 69(1) mJ mol −1 K −2 , β = 11.6(2) mJ mol −1 K −4 (corresponding to θ cal D = 169(1) K, which obviously strongly deviates from previously published values [21] due to the inclusion of the additional terms), δ = 0.37(2) mJ mol −1 K −6 , and ε = −5.3( 7) μJ mol −1 K −8 . 3), which is slightly larger than that of the weak-coupling BCStheory limit (i.e., 1.43) for s-wave superconductors.…”

“…Here it should be noted that the description of the low-temperature phonons is a typical problem of 5:6:18 stannides. To model c ph for Sc 5 Ru 6 Sn 18 Kumar et al [21] fitted c p to γ T + βT 3 + δT 5 above T c = 3.5 K. A comparison of the value of γ = 51.1 mJ mol −1 K −2 obtained in [15] for Sc 5 Rh 6 Sn 18 with Fig. 2(a) in this work hints at its underestimation.…”

“…Tm 5 Rh 6 Sn 18 (T c = 2.2 K) is characterized by the coexistence of magnetism and reentrant superconductivity at zero magnetic field [20]. In contrast, conventional BCS superconductivity with an swave gap is observed for Sc 5 Ru 6 Sn 18 (T c = 3.5 K, B c2 = 2.6 T) [21] and Sc 5 Ir 6 Sn 18 (T c = 2.64 K, B c2 = 3.2 T) [22]. Interestingly, recent field-dependent low-temperature thermal conductivity measurements showed nodeless s-wave gaps for both Y 5 Rh 6 Sn 18 and Lu 5 Rh 6 Sn 18 [23].…”

Superconductivity of structurally disordered Y5Ir6Sn18

“…Furthermore, the Drude model for the free electron gas is applied to obtain the mean free path l = v F τ = v F ρ 0 ne 2 /m* = 3.5 (5) nm, with the mean free scattering time τ = m*/ρ 0 ne 2 = 3.1(2) × 10 −14 s. Currently, since the relation l/ξ GL = 0.28 < 1, one has to conclude that the superconductivity of Y 5 Ir 6 Sn 18 is at a moderately dirty limit, similar to that observed for Sc 5 Ru 6 Sn 18 . 17 In the inset of Fig. 8, the Sommerfeld coefficients γ(B) for Y 5 Ir 6 Sn 18 are plotted against the applied fields.…”

“…16 In addition, some other representatives of this class of compounds [ e.g. Sc 5 Ru 6 Sn 18 ( T c = 3.5 K), 17 Sc 5 Ir 6 Sn 18 ( T c = 2.64 K) 18 and Lu 5 Ir 6 Sn 18 ( T c = 3.0 K) 4 ] were recently shown to be conventional s -wave BCS-like SCs.…”