Microscopic properties of the heavy-fermion superconductor PuCoIn5 explored by nuclear quadrupole resonance

We report ^115 In nuclear quadrupolar resonance (NQR) measurements on the heavy-fermion superconductor PuCoIn _5 , in the temperature range 0.29K ≤ T ≤ 75K. The NQR parameters for the two crystallographically inequivalent In sites are determined, and their temperature dependence is investigated. A linear shift of the quadrupolar frequency with lowering temperature below the critical value T _c is revealed, in agreement with the prediction for composite pairing . The nuclear spin–lattice relaxation rate T _1 ^−1 ( T ) clearly signals a superconducting (SC) phase transition at T _c ≃ 2.3 K, with strong spin fluctuations, mostly in-plane, dominating the relaxation process in the normal state near to T _c . Analysis of the T _1 ^−1 data in the SC state suggests that PuCoIn _5 is a strong-coupling d -wave superconductor.