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

TL;DR

This study investigates the nuclear spin-lattice relaxation rates in PuRhGa$_5$ and PuCoGa$_5$, revealing d-wave superconductivity with impurity effects and contrasting normal-state behaviors linked to magnetic fluctuations and pseudogap formation.

Contribution

It provides the first detailed comparison of relaxation rates and Knight shifts in these compounds, proposing a unified model for their magnetic and superconducting properties.

Findings

Both compounds exhibit d-wave superconducting gaps with impurity scattering effects.

PuRhGa$_5$ shows a suppression of relaxation rate below 25 K in the normal state.

PuCoGa$_5$ displays a monotonic increase in relaxation rate down to T_c.

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.