Nuclear spin-lattice relaxation rate in PuMGa5 (M=Rh, Co):: A two-component spin-fermion model

We examine the nuclear spin-lattice relaxation rates 1/T-1 of PuRhGa5 and PuCoGa5, both in the superconducting and normal states, as well as their Knight shifts. Results for both compounds are consistent with a superconducting gap of d-wave symmetry in the presence of strong impurity scattering, though with quite different gap-over-T-c ratios 2 Delta(0)/k(B)T(c) (eight for PuCoGa5 and five for PuRhGa5). In the normal state, PuRhGa5 exhibits a gradual suppression of (T1T)(-1) below 25 K, while measurements for PuCoGa5 reveal a monotonic increase down to T-c. We propose that this behavior is consistently understood by the crossover of the two-dimensional quantum antiferromagnetic correlation of the local 5f-electron spins of Pu and the concomitant formation of the fermion pseudogap based on the two-component spin-fermion model.