muSR linewidth and isotropic pairing in superconducting PrOs4Sb12
  Transverse-field muon spin rotation measurements in the vortex-lattice mixed state of the heavy-fermion (HF) superconductor PrOs4Sb12 yield a temperature dependence of the penetration depth indicative of an isotropic or nearly isotropic energy gap. This is not seen to date in any other HF superconductor and is a signature of isotropic pairing symmetry, possibly related to a novel nonmagnetic "quadrupolar Kondo" HF mechanism in PrOs4Sb12. The T = 0 relaxation rate \sigma_s(0) = 0.91(1) \mu s^-1 yields an estimated penetration depth \lambda(0) = 3440(20) \AA, which is considerably shorter than in other HF superconductors. 
D. E. MacLaughlin, J. E. Sonier, R. H. Heffner, O. O. Bernal, B.-L.   Young, M. S. Rose, G. D. Morris, E. D. Bauer, T. D. Lo...