Np nuclear relaxation rate in heavy fermion superconductor NpPd Al

重い電子系超伝導体NpPd AlにおけるNpの核磁気緩和率

中堂 博之 ; 徳永 陽  ; 神戸 振作  ; 酒井 宏典   ; 芳賀 芳範   ; 松田 達磨; 大貫 惇睦; 安岡 弘志; 青木 大*; 本間 佳哉*; Walstedt, R. E.*

Chudo, Hiroyuki; Tokunaga, Yo; Kambe, Shinsaku; Sakai, Hironori; Haga, Yoshinori; Matsuda, Tatsuma; Onuki, Yoshichika; Yasuoka, Hiroshi; Aoki, Dai*; Homma, Yoshiya*; Walstedt, R. E.*

Al nuclear spin-lattice relaxation rate 1/ has been measured in heavy fermion superconductor NpPdAl for a wide range of external fields between 0.7 and 11 T. We found that 1/ exhibits a strong, field-dependent behavior at low fields below 3 T, which is attributed to unlike-spin cross relaxation between Np and Al. An analysis based on the cross relaxation process allows us to make the first quantitative estimates of the Np nuclear relaxation rate 1/ in an itinerant 5 electron system. The estimated values of 1/ 6 10 s, with a weak temperature variation, are below the resolution of NMR relaxation times, indicating that a direct observation of the Np NMR signal would be very difficult, at least in the paramagnetic state. It is proposed that a direct observation of Np NMR might be possible in the superconducting state at 1K.