NMR studies of actinide dioxides

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

In this paper, we present our recent NMR works on Neptunium and Plutonium compounds. In order to elucidate the nature of the exotic multipolar ordered phase of NpO, we have initiated the first NMR measurements on this system. We have shown that direct observation of multipole order parameters is possible by means of NMR. Our NMR results provide further insight into the microscopic nature of multipole phase transitions in f-electron systems. We have also performed Ga NMR/NQR studies on a single crystal of PuRhGa. From the temperature dependence of the spin-lattice relaxation rate (), we have found that PuRhGa is an unconventional superconductor having an anisotropic superconducting (SC) gap 2=5. Furthermore, we have confirmed the Knight shift to be decreased below . This gives strong evidence for spin singlet SC pairing.