K. Ohishi, R.H. Heffner, 2 G.D. Morris, 3 E.D. Bauer, M.J. Graf, J.-X. Zhu, L.A. Morales, J.L. Sarrao, M.J. Fluss, D.E. MacLaughlin, L. Shu, W. Higemoto, and T.U. Ito 6 Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195, Japan Los Alamos National Laboratory, Los Alamos, New Mexico 87545 USA TRIUMF, 4004 Wesbrook Mall, Vancouver, B.C., Canada V6T 2A3 Lawrence Livermore National Laboratory, P.O. Box 808, Livermore, California 94550 USA Department of Physics, University of California, Riverside, California 92521 USA Department of Physics, Tokyo Institute of Technology, Megro-ku, Tokyo 152-8551, Japan (Dated: May 31, 2018)

K. Ohishi,1,* R. H. Heffner,1,2 T. U. Ito,1,3 W. Higemoto,1 G. D. Morris,2,4 N. Hur,5 E. D. Bauer,2 J. L. Sarrao,2 J. D. Thompson,2 D. E. MacLaughlin,6 and L. Shu6,† 1Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195, Japan 2Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA 3Department of Physics, Tokyo Institute of Technology, Meguro-ku, Tokyo 152-8551, Japan 4TRIUMF, 4004 Wesbrook Mall, Vancouver, British Columbia, Canada V6T 2A3 5Department of Physics, Inha University, Incheon 402-751, Korea 6Department of Physics, University of California, Riverside, California 92521, USA Received 3 June 2009; revised manuscript received 9 August 2009; published 8 September 2009

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.

We report μSR Knight shift and susceptibility studies for 1 T applied field along the crystalline cand a-axes of the heavy fermion compound Ce2IrIn8. Below a characteristic temperature T ∗ one observes a ‘Knight-shift anomaly’ in which the Knight shift constant K no longer scales linearly with χ. This anomaly is consistent with a scaling law in which the susceptibility χ is composed of a high-temperature component corresponding to non-interacting local moments and a low-temperature component χcf ∼ (1 − T/T ∗) ln(T ∗/T ) which characterizes the heavy-electron state below T ∗. We find that T ∗ is anisotropic, with T ∗ a = 59(3) K and T ∗ c = 24(1) K, and derive the magnitudes of χ cf .

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 σ_s(0) = 0.91(1) μs^-1 yields an estimated penetration depth λ(0) = 3440(20) Å, which is considerably shorter than in other HF superconductors.