The nuclear spin-lattice relaxation rate in the PuMGa${}_5$ materials

Abstract

We examine the nuclear spin-lattice relaxation rates $1/T_1$ of PuRhGa${}_5$ and PuCoGa${}_5$, 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 $2{\Delta }_0/k_B{T}_c$ (8 for PuCoGa${}_5$ and 5 for PuRhGa${}_5$). In the normal state, PuRhGa${}_5$ exhibits a gradual suppression of $(T_{1}T{)}^{-1}$ below 25 K, while measurements for PuCoGa${}_5$ reveal a monotonic increase down to $T_c$. We propose that this behavior is consistently understood by the crossover from the two-dimensional quantum antiferromagnetic regime of the local $5f$-electron spins of Pu to the concomitant formation of the fermion pseudogap based on the two-component spin-fermion model.

7 pages, 6 figures, minor changes and references added

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