Anisotropy of antiferromagnetic spin fluctuations in the heavy fermion superconductors of CeIn and PuGa (=Co, Rh)

重い電子系超伝導体CeInとPuGa (=Co, Rh)における反強磁性スピン揺らぎの異方性

酒井 宏典   ; 神戸 振作  ; 徳永 陽  ; 芳賀 芳範   ; Baek, S.-H.*; Ronning, F.*; Bauer, E. D.*; Thompson, J. D.*

Sakai, Hironori; Kambe, Shinsaku; Tokunaga, Yo; Haga, Yoshinori; Baek, S.-H.*; Ronning, F.*; Bauer, E. D.*; Thompson, J. D.*

重い電子系CeInとPuGa (=Co, Rh)において、核磁気共鳴(NMR)法を用いて微視的に反強磁性スピン揺らぎの異方性を調べた。ナイトシフトと核スピン格子緩和率のデータは、これらの非通常型超伝導体の通常状態におけるXY型の異方性を示唆した。さらに、正方晶115型超伝導体では、常伝導体であるUFeGaや反強磁性体UPtGaや、NpCoGa, NpFeGaなどに比べて、その異方性は大きくなっており、XY型の反強磁性揺らぎの強い系ほど超伝導転移温度が高いということがわかった。

The anisotropy of antiferromagnetic spin fluctuations has been investigated microscopically in the heavy fermion systems of CeIn and PuGa (=Co, Rh) by means of nuclear magnetic resonance (NMR). Both systems are known to be relatively high- superconductors among the heavy fermion systems, especially PuCoGa, which has a =18.5 K almost one order of magnitude larger than for CeCoIn (=2.3 K). Analysis of the Knight shift and spin-lattice relaxation rates suggests XY-type anisotropy in the antiferromagnetic spin fluctuations in the normal states of these unconventional superconductors. Moreover, the 115 superconductors with larger XY-type fluctuations have a higher , compared with the anisotropy of spin fluctuations in the related paramagnetic system UFeGa and antiferromagnets UPtGa, NpCoGa, NpFeGa.