Penetration depth, symmetry breaking, and gap nodes in superconducting   PrOs4Sb12
  Transverse-field muon spin relaxation rates in single crystals of the heavy-fermion superconductor PrOs4Sb12 (Tc = 1.85 K) are nearly constant in the vortex state for temperatures below ~0.5Tc. This suggests that the superconducting penetration depth lambda(T) is temperature-independent at low temperatures, consistent with a gapped quasiparticle excitation spectrum. In contrast, radiofrequency measurements yield a stronger temperature dependence of lambda(T), indicative of point nodes in the gap. A similar discrepancy exists in superconducting Sr2RuO4 which, like PrOs4Sb12, breaks time-reversal symmetry (TRS) below Tc, but not in a number of non-TRS-breaking superconductors. 
Lei Shu, D. E. MacLaughlin, R. H. Heffner, G. D. Morris, O. O. Bernal,   F. Callaghan, J. E. Sonier, A. Bosse, J. E. Anderso...