Ga NQR relaxation rates in superconductor PuRhGa

超伝導体PuRhGaにおけるGa核四重極共鳴緩和率

酒井 宏典   ; 神戸 振作  ; 徳永 陽  ; 藤本 達也; Walstedt, R. E.*; 安岡 弘志; 青木 大*; 本間 佳哉*; 山本 悦嗣  ; 中村 彰夫; 塩川 佳伸*; 中島 邦久  ; 荒井 康夫; 松田 達磨; 芳賀 芳範   ; 大貫 惇睦*

Sakai, Hironori; Kambe, Shinsaku; Tokunaga, Yo; Fujimoto, Tatsuya; Walstedt, R. E.*; Yasuoka, Hiroshi; Aoki, Dai*; Homma, Yoshiya*; Yamamoto, Etsuji; Nakamura, Akio; Shiokawa, Yoshinobu*; Nakajima, Kunihisa; Arai, Yasuo; Matsuda, Tatsuma; Haga, Yoshinori; Onuki, Yoshichika*

最近見つかったプルトニウム化合物超伝導体はその高い超伝導転移温度から非常に注目されている。われわれは、PuRhGaにおいて、核磁気共鳴(NMR/NQR)を用いた研究を行っている。結晶学的に異なる2つのGa位置について、おのおのに対応するNQR信号を発見し、NQR緩和率測定を行った。その結果から、スピン揺らぎの異方性についての情報を得た。

A lot of attention is currently focused on Pu-based superconductors. These systems have relatively high superconducting (SC) transition temperatures, 18 K for PuCoGa and 9 K for PuRhGa. Both compounds crystallize in the tetragonal HoCoGa (115) structure, which is well known for the heavy-fermion SC systems CeIn (=Co, Rh, Ir)with 2 K at most. Recently, NMR and NQR experiments have been reported for PuCoGa by Curro et al. and for PuRhGa by our group. In both cases, measurements of using NQR have revealed that the Pu115 superconductors show unconventional superconductivity with an anisotropic gap. Now we have measured the more detailed data of for NQR lines in PuRhGa, especially focusing on the low-lying magnetic excitation in the normal state. From the viewpoint of spin-fluctuations, we will discuss the difference between PuRhGa and PuCoGa and between superconducting Pu115 and non-superconducting An115 series.