Superconducting Characteristics of Filled Skutterudites LaPt₄Ge₁₂ and PrPt₄Ge₁₂: ⁷³Ge-NQR/NMR Studies

Abstract

We report on the superconducting characteristics of the filled skutterudites LaPt 4 Ge 12 ( T c =8.3 K) and PrPt 4 Ge 12 ( T c =7.9 K) by 73 Ge-nuclear quadrupole resonance (NQR) at a zero field. In PrPt 4 Ge 12 , the nuclear spin–lattice relaxation rate 73 (1/ T 1 ) has revealed a coherence peak just below T c , indicating that the superconductivity of PrPt 4 Ge 12 is accounted for in terms of the conventional BCS regime. The result was consistently reproduced by not only an isotropic s -wave gap model but also an anisotropic s -wave gap model with a point node. In the conventional superconductor LaPt 4 Ge 12 , the coherence peak in 73 (1/ T 1 ) is markedly suppressed owing to some damping effect of quasiparticles. We note that the T c s of LaPt 4 Ge 12 and PrPt 4 Ge 12 being higher than that of other R Pt 4 Ge 12 may be attributed to the larger density of states, not to some local anharmonic phonon modes derived from the possible rattling of R ions.