We report on novel antiferromagnetic (AFM) and superconducting (SC) properties of noncentrosymmetric CePt3Si through measurements of the 195Pt nuclear spin-lattice relaxation rate 1/T(1). In the normal state, the temperature (T) dependence of 1/T(1) unraveled the existence of low-lying levels in crystal-electric-field multiplets and the formation of a heavy-fermion (HF) state. The coexistence of AFM and SC phases that emerge at T(N)=2.2 K and T(c)=0.75 K, respectively, takes place on a microscopic level. CePt3Si is the first HF superconductor that reveals a peak in 1/T(1) just below T(c) and, additionally, does not follow the T3 law that used to be reported for most unconventional HF superconductors. We remark that this unexpected SC characteristic may be related to the lack of an inversion center in its crystal structure.

We report Sb-NQR results which evidence a heavy-fermion (HF) behavior and an unconventional superconducting (SC) property in Pr(Os4Sb12 with T(c)=1.85 K. The temperature (T) dependence of nuclear-spin-lattice-relaxation rate, 1/T(1), and NQR frequency unravel a low-lying crystal-electric-field splitting below T0 approximately 10 K, associated with Pr3+(4f(2))-derived ground state. In the SC state, 1/T(1) shows neither a coherence peak just below T(c) K nor a T3-like power-law behavior observed for anisotropic HF superconductors with the line-node gap. The isotropic energy gap with its size Delta/k(B)=4.8 K seems to open up across T(c) below T(*) approximately 2.3 K. It is surprising that Pr(Os4Sb12 looks like an isotropic HF superconductor-it may indeed argue for Cooper pairing via quadrupolar fluctuations.

We report the measurements of the 29 Si Knight shift 29 K on the noncentrosymmetric heavyfermion compound CePt3Si in which antiferromagnetism (AFM) with TN = 2.2 K coexists with superconductivity (SC) with Tc = 0.75 K. Its spin part 29 Ks, which is deduced to be K c s ≥ 0.11 and 0.16% at respective magnetic fields H = 2.0061 and 0.8671 T, does not decrease across the superconducting transition temperature Tc for the field along the c-axis. The temperature dependence of nuclear spin-lattice relaxation of 195 Pt below Tc has been accounted for by a Cooper pairing model with a two-component order parameter composed of spin-singlet and spin-triplet pairing components. From this result, it is shown that the Knight-shift data are consistent with the occurrence of the two-component order parameter for CePt3Si. KEYWORDS: heavy-fermion superconductivity, CePt3Si, NMR, Knight shift, Cooper pairing symmetryThe recent discovery of superconductivity (SC) in the noncentrosymmetric heavy-fermion (HF) compound CePt 3 Si has initiated much interest, 1 because experimental data revealed various intriguing features.2-6 One of the novel superconducting characteristics of CePt 3 Si is that the upper critical field H c2 is significantly large, suggesting an extrapolated value of H c2 ∼ 3 − 5 T, 3-5 times larger than the Pauli limit of H c2 estimated from the relation H P ≈ ∆/ √ 2µ B ≈ 1 T. A recent theoretical calculation revealed that such an enhancement of H c2 is characteristic for the noncentrosymmetric SC in which the Cooper pairs are predominant in spin-triplet configurations.7 Another novel aspect is that a possible formation of spin-triplet pairing is realized under the uniform coexistence of antiferromagnetism (AFM) and SC, which was confirmed from the measurements of 195 Pt nuclear spin-lattice relaxation rate 1/T 1 , muon spin rotation, and neutron scattering. 2-4With respect to the superconducting characteristics, most remarkably, the results of 195 Pt 1/T 1 , 2 have revealed that CePt 3 Si is the first HF superconductor that exhibits a peak in 1/T 1 just below T c and it does not follow the T 3 law for most unconventional HF superconductors. 8,9 This unexpected nature of SC is related to the absence of an inversion center in its crystal structure. To account for the experimentally observed features of the peak in 1/T 1 just below T c 2 and a line-node gap behavior at low temperatures detected by the measurements of London penetration depth 5 and thermal conductivity, 6 a novel Cooper pairing model has been developed by assuming a two-component order parameter composed of *

We report on novel superconducting characteristics of the heavy fermion (HF) superconductor CePt3Si without inversion symmetry through 195 Pt-NMR study on a single crystal with Tc = 0.46 K that is lower than Tc ∼ 0.75 K for polycrystals. We show that the intrinsic superconducting characteristics inherent to CePt3Si can be understood in terms of the unconventional strong-coupling state with a line-node gap below Tc = 0.46 K. The mystery about the sample dependence of Tc is explained by the fact that more or less polycrystals and single crystals inevitably contain some disordered domains, which exhibit a conventional BCS s-wave superconductivity (SC) below 0.8 K. In contrast, the Néel temperature TN ∼ 2.2 K is present regardless of the quality of samples, revealing that the Fermi surface responsible for SC differ from that for the antiferromagnetic order. These unusual characteristics of CePt3Si can be also described by a multiband model; in the homogeneous domains, the coherent HF bands are responsible for the unconventional SC, whereas in the disordered domains the conduction bands existing commonly in LaPt3Si may be responsible for the conventional s-wave SC. We remark that some impurity scatterings in the disordered domains break up the 4f-electrons-derived coherent bands but not others. In this context, the small peak in 1/T1 just below Tc reported in the previous paper (Yogi et al, (2004)) is not due to a two-component order parameter composed of spin-singlet and spin-triplet Cooper pairing states, but due to the contamination of the disorder domains which are in the s-wave SC state.as compared to a Pauli limiting field. 15-17) This kind of behavior has never been observed in the other HF superconductors such as CeCoIn 5 , CeIrIn 5 , and CeCu 2 Si 2 , which are in a spin-singlet Cooper pairing regime. In the noncentrosymmetric superconductors where the correlation between electrons may be not so significant, however, the characteristic feature for conventional s-wave spin singlet superconducting state has been observed in many compounds, for example, Y 2 C 3 , 18, 19) Ir 2 Ga 9 , 20, 21) LaPt 3 Si, 22) LaIrSi 3 , 23) Li 2 Pd 3 B, 24) and so on, whereas the parity mixing state has been argued only in the related compound Li 2 Pt 3 B. 25,26) The CePt 3 Si exhibits superconductivity at T c = 0.75 K in an antiferromagnetically ordered state below a Néel temperature of T N = 2.2 K, as reported by Bauer et al. 9,27) Neutron-scattering measurement probed an AFM structure with a wave vector Q = (0, 0, 1/2) and a magnetic moment of 0.16µ B lying in the ab-plane of the tetragonal lattice. 28) Uniform coexistence of the AFM order and SC has been microscopically evidenced by NMR 29, 30) and µSR. 31) Although CePt 3 Si has attracted considerable attention as the first superconductor without inversion symmetry, 3-8) the experimental results are still contradictory. For example, the London penetration depth, 32) thermal conductivity, 33) and NMR 29) revealed J. Phys. Soc. Jpn.