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 ThPt ₄Ge₁₂. 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 ThPt₄Ge ₁₂. 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* ≈ 4.5m _e, and the superfluid carrier density, n_s ≈ 1.06 × 10²⁸ carriers m^-3. We found a marked difference between the zero-field cooling and field-cooled vortex state muon spin relaxation rates, σ_s(T ), below the irreversibility temperature, T_ir ∼ 2.5 K. A linear field dependence of σ_s(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.