Multiband Superconductivity in Heavy Fermion Compound CePt3Si without Inversion Symmetry: An NMR Study on a High-Quality Single Crystal

Abstract

We report on novel superconducting characteristics of the heavy fermion (HF) superconductor CePt 3 Si without inversion symmetry through 195 Pt-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 3 Si 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 3 Si 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 3 Si may be responsible for the conventional s -wave SC. We remark that some impurity scatterings in the disordered domains break up the 4 f -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.