Muon spin rotation and relaxation studies of the filled skutterudite superconductor ThPt4Ge12

Longitudinal and transverse field muon spin rotation/relaxation measurements have been carried out on a polycrystalline sample of ThPt4Ge12. The zero-field measurements in the longitudinal geometry do not reveal any signature of a spontaneous internal magnetic field below the superconducting transition temperature, indicating the preservation of time-reversal symmetry in the superconducting state of ThPt4Ge12. From the transverse field data, the zero field magnetic penetration depth, λ(0), was estimated to be 110(15) nm, and then we have estimated the effective mass of the quasiparticles, m*∼4.5me, and the superfluid carrier density, ns∼1.06 x 1028 carriers m-3. We found a marked difference between the zero-field cooling and field-cooled vortex state muon spin relaxation rates, σs(T), below the irreversibility temperature, Tir ∼ 2.5 K. A linear field dependence of σs(H) and power law behaviour of σs(T) exhibit a significant deviation from those expected for isotropic BCS-superconductors. The analysis of correlation between the superconducting transition temperature and the effective Fermi temperature within the Uemura classification scheme reveals that the condensation energy in ThPt4Ge12 is comparable to those of exotic superconductors.