1. Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
2. Department of Physics, Chonnam National University, Kwangju 500-757, Korea

Correspondence to: N. J. Curro¹ Correspondence and requests for materials should be addressed to N.J.C. (Email: curro@lanl.gov).

In the Bardeen–Cooper–Schrieffer theory of superconductivity, electrons form (Cooper) pairs through an interaction mediated by vibrations in the underlying crystal structure. Like lattice vibrations, antiferromagnetic fluctuations can also produce an attractive interaction creating Cooper pairs, though with spin and angular momentum properties different from those of conventional superconductors. Such interactions have been implicated for two disparate classes of materials—the copper oxides^{1, 2} and a set of Ce- and U-based compounds³. But because their transition temperatures differ by nearly two orders of magnitude, this raises the question of whether a common pairing mechanism applies. PuCoGa₅ has a transition temperature intermediate between those classes and therefore may bridge these extremes⁴. Here we report measurements of the nuclear spin-lattice relaxation rate and Knight shift in PuCoGa₅, which demonstrate that it is an unconventional superconductor with properties as expected for antiferromagnetically mediated superconductivity. Scaling of the relaxation rates among all of these materials (a feature not exhibited by their Knight shifts) establishes antiferromagnetic fluctuations as a likely mechanism for their unconventional superconductivity and suggests that related classes of exotic superconductors may yet be discovered.

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