Al NMR evidence for the strong-coupling -wave superconductivity in NpPdAl

Chudo, Hiroyuki ; Sakai, Hironori   ; Tokunaga, Yo  ; Kambe, Shinsaku  ; Aoki, Dai*; Homma, Yoshiya*; Shiokawa, Yoshinobu*; Haga, Yoshinori   ; Ikeda, Shugo*; Matsuda, Tatsuma; Onuki, Yoshichika; Yasuoka, Hiroshi

We present Al NMR studies for a single crystal of the newly developed superconductor NpPdAl ( K). In the superconducting state, the Al NMR spectrum shifts to lower frequencies owing to a decrease of the spin part of the Knight shift, and exhibits broadening characteristic of the local field distribution associated with a vortex lattice. We have also found that the Al nuclear spin-lattice relaxation rate () decreases just below with no coherence peak and shows behavior at low temperatures. The observed temperature dependences of the Knight shift and in general accord with those assuming a line-node superconducting gap with the gap value of . Therefore, the present NMR data provides evidence for strong-coupling -wave superconductivity in NpPdAl.