Flux Pinning and Anisotropic Gap Function in Sc₅Ru₆Sn₁₈ Superconducting Crystals
Dinesh Kumar1*, C. N. Kuo1, M. K. Lee2, C. S. Lue1, L. J. Chang1
1Department of Physics, National Cheng Kung University, Tainan, Taiwan
2Instrumentation Center, National Cheng Kung University, Tainan, Taiwan
* presenting author:Dinesh Kumar, email:dineshdixit@mail.ncku.edu.tw
We have performed low temperature (down to 1.8 K) dc magnetization, specific heat and muon spin relaxation (μSR) measurements on Sc₅Ru₆Sn₁₈ superconducting single crystals, with Tc ~ 3.5 K. We have obtained the critical current density (Jc) as a function of magnetic field, from the isothermal dc magnetization curves using a Bean model [1,2], Jc = 20ΔM/[a(1-a/3b)]. The Jc strongly depends on the magnetic field, where Jc shows a peak at very low fields followed by exponential decrease and at high fields Jc shows the power law (H^a) decrease with increase in the field. At 1.8 K, the maximum value of Jc is ~ 6×10⁸ A/m² at a low field of 150 Oe. A long coherence length (~15 nm) is observed at 1.8 K, which indicates the pinning energy of the vortices is high. The thermodynamic irreversibility field is comparable to the upper critical field (Hc₂), which is quite possible as the material has low Tc and high coherence length. The T³ dependence of electronic heat capacity (Ce) below Tc, at zero magnetic field, clearly indicates that Sc₅Ru₆Sn₁₈ has an anisotropic superconducting gap with a point node similar to the case of Y₅Rh₆Sn₁₈ [3]. The H^0.5 dependence of electronic heat capacity coefficient (γ) confirms the existence of point-node in the superconducting gap of Sc₅Ru₆Sn₁₈. The time reversal symmetry breaking in Sc₅Ru₆Sn₁₈ has been studied using zero-field μSR measurements, however, no spontaneous internal magnetic field was observed in this material and hence we did not observe broken time reversal symmetry in this superconductor.


References:
1. C. P. Bean, Phys. Rev. Letters, 8, 250 (1964).
2. C. P. Bean, Rev. Modern Phys. 36, 31–39 (1964).
3. K. Inoue, H. Hayamizu, J. Akimitsu, Proc. Int. Conf. Heavy Electrons (ICHE2010), J. Phys. Soc. Jpn. 80, SA112 (2011).


Keywords: Superconductivity, Flux pinning, Muon Spin Relaxation, Criticial field, Heat capacity