Multiband superconductivity in heavy fermion compound CePt ₃Si without inversion symmetry: An NMR study on a high-quality single crystal

We report on novel superconducting characteristics of the heavy fermion (HF) superconductor CePt ₃Si without inversion symmetry through ¹⁹⁵Pt-NMR study on a single crystal with T _c = 0.46 K that is lower than T _c ∼ 0.75 K for polycrystals. We show that the intrinsic superconducting characteristics inherent to CePt ₃Si can be understood in terms of the unconventional strong-coupling state with a line-node gap below T _c = 0.46 K. The mystery about the sample dependence of T _c 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 T _N ∼ 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 CePt ₃Si 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 LaPt ₃Si 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/T ₁ just below T _c reported before [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.