A combined study of the structural and electronic properties of polycrystalline ${\mathrm{Pu}}_2{\mathrm{C}}_3$ is reported based on x-ray diffraction, specific heat, magnetic susceptibility, and ${}^{13}\mathrm{C}$ nuclear magnetic resonance (NMR). X-ray diffraction reveals a global noncentrosymmetric cubic lattice, with a nearest-neighbor C–C bond length of $r=1.38$ Å. ${}^{13}\mathrm{C}$ NMR measurements indicate that the global cubic symmetry is locally broken, revealing two unique carbon environments. Magnetic susceptibility suggests enhanced Pauli paramagnetism, and specific heat reveals a moderately large electronic Sommerfeld coefficient $\gamma =45\mathrm{mJ}{\mathrm{mol}}_{\mathrm{Pu}}^{-1}{\mathrm{K}}^{-2}$, with a Wilson ratio $R_W\approx 1.3$ further indicating moderate correlations. ${}^{13}\mathrm{C}$ nuclear spin-lattice relaxation rate ($1/T_1$) and Knight shift ($K$) measurements find metallic Korringa behavior (i.e., $T_{1}T{K}^2=\text{const.}$) with modest ferromagnetic spin fluctuations at low temperature. Taken together, the data point to a delocalized nature of a narrow $5f$-electron band with electronic correlations. Our data provide prime evidence for a plutonium-based metallic system with electronic correlations, which sheds new light on the understanding of complex paramagnetism in actinide-based metallic compounds.

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• Magnetic susceptibility
• Paramagnetism
• Specific heat
• Actinides
• Density functional calculations
• Nuclear magnetic resonance