Inelastic quasiparticle scattering and T1 -1 NQR relaxation rate in Pr1-x Lax Os4 Sb12

We present an analysis of recent Sb-NQR measurements of the heavy-fermion superconductor PrOs4 Sb12 and the related La-doped series of superconductors Pr1-x Lax Os4 Sb12. We find that this data, along with previous temperature-dependent superfluid density results and are well described by a strong-coupling order parameter containing a doping-dependent proportion of the first cubic harmonic (kx4 + ky4 + kz4) component along with an s -wave component, when inelastic scattering due to Coulomb effects are taken into account. The resulting gap function has deep minima along the cubic axis [100], etc. but no nodes. We use the order parameter fits to generate, within the Ginzburg-Landau theory, the effective thermal mass enhancement relative to the LaOs4 Sb12 material and find that it rapidly varies for small x.