Superconducting gap structure of the skutteruditeLaPt4Ge12probed by specific heat and thermal transport

Abstract

We investigated the superconducting order parameter of the filled skutterudite LaPt4Ge12, with a transition temperature of Tc = 8.3 K. To this end, we performed temperature and magnetic-field dependent specific-heat and thermal-conductivity measurements. All data are compatible with a single superconducting s-wave gap. However, a multiband scenario cannot be ruled out. The results are discussed in the context of previous studies on the substitution series Pr1−xLaxPt4Ge12. They suggest compatible order parameters for the two end compounds LaPt4Ge12 and PrPt4Ge12. This is not consistent with a single s-wave gap in LaPt4Ge12 considering previous reports of unconventional and/or multiband superconductivity in PrPt4Ge12.

Transport and Point Contact Measurements on Pr1−xCexPt4Ge12 Superconducting Polycrystals

“…The red solid line in Figure 2 b represents the best fit of the data by the Ginzburg–Landau (G-L) formula: where H c 2 (0) is the upper critical field at zero temperature and is the reduced temperature. The data are very well described by the G-L Equation with μ 0 H c 2 (0) = 1.23 T, as already reported for (Pr,La)Pt 4 Ge 12 and Pr 1−x Nd x Pt 4 Ge 12 compounds [ 14 , 24 , 29 , 31 , 32 , 33 , 34 ]. For comparison, in Figure 2 b, we also show the temperature dependence of the upper critical field derived within the Werthamer–Helfand–Hohenberg (WHH) model (blue dashed line), which includes orbital and Zeeman pair breaking [ 35 , 36 ].…”

“…μSR experiments on PrPt 4 Ge 12 showed a time-reversal symmetry breaking below T c [ 20 , 21 , 22 , 23 ], in contrast to the results on LaPt 4 Ge 12 , for which the time-reversal symmetry breaking is absent and a conventional superconductivity with a fully gapped density of states is supposed [ 21 ]. The superconducting order parameter of LaPt 4 Ge 12 has also been studied using specific heat and thermal conductivity measurements [ 24 ], showing that the sharp transition in the specific heat and its zero-field temperature dependence are well described in a conventional BCS (Bardeen–Cooper–Schrieffer) scenario characterized by a single energy gap and s-wave symmetry [ 25 ]. On the other hand, de Haas–van Alphen measurements have been reported with state-of-the-art band-structure calculations showing that LaPt 4 Ge 12 and PrPt 4 Ge 12 have almost identical electronic structures, Fermi surfaces and effective masses [ 26 ].…”

Recent progress on superconductors with time-reversal symmetry breaking

“…The early measurements of the spe-cific heat and µSR suggest nodal superconductivity for PrPt 4 Ge 12 104 . Later measurements of the London penetration depth 105,106 , specific heat, thermal transport 92 , NQR 107 and photoemission spectroscopy 108 demonstrate that both PrPt 4 Ge 12 and LaPt 4 Ge 12 behave more like conventional BCS SCs with a fully opened energy gap. The smooth evolution of the superconducting transition between the Pr-based end compounds with TRS breaking, and the time reversal preserving La-based materials, is difficult to account for and requires further studies.…”

Electron-phonon superconductivity in the filled skutterudites LaRu4P12, LaRu4As12 , and Tütüncü1, Karaca2, Srivastava3 2017Phys. Rev. B

“…This discovery is very interesting because, so far, X elements are restricted to volatile and toxic pnictogens (X = P, As, Sb) rather than Ge. Furthermore, new germanium-platinum compounds LaPt 4 Ge 12 and PrPt 4 Ge 12 with the filled-skutterudite crystal structure have been synthesized by experimenters [49][50][51][52][53][54]. Magnetic susceptibility, specific heat, and electrical resistivity measurements indicate superconductivity in LaPt 4 Ge 12 and PrPt 4 Ge 12 below 8.3 K [49].…”