Superconducting state of filled-skutterudite RPt4Ge12 (R = La, Pr): 73Ge-NQR studies

We report Ge-73-NQR studies on filled-skutterudite superconductors LaPt4Ge12 and PrPt4Ge12 under zero external field. In PrPt4Ge12, the measurement of the nuclear spin-lattice relaxation rate 1/T-1 has revealed a distinct coherence peak just below T-c followed by an exponential decrease well below T-c, evidencing that PrPt4Ge12 is an s-wave superconductor with the isotropic gap in a weak-coupling regime. In LaPt4Ge12, the 1/T-1 exhibits the exponential decrease well below T-c, suggesting the isotropic s-wave superconductivity. Even though Ge-73-NQR-1/T-1 in LaPt4Ge12 has been measured under zero field, its coherence peak was absent, which contrasts with the result in Pr-compound. This may point to a possible anisotropy in the Fermi surface and/or some damping effect of quasiparticles in association with electron-phonon interactions. (C) 2009 Elsevier B.V. All rights reserved.