A combined study of the structural and electronic properties of polycrystalline Pu₂C₃ is reported based on x-ray diffraction, specific heat, magnetic susceptibility, and ^13C 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. ^13C 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 =450. 16em{0ex}mJ0. 16em{0ex}molₔ^-10. 16em{0ex}K^-2, with a Wilson ratio Rₖ1. 3 further indicating moderate correlations. ^13C nuclear spin-lattice relaxation rate (1/T₁) and Knight shift (K) measurements find metallic Korringa behavior (i. e. , T₁TK^2=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.
Yamamoto et al. (Wed,) studied this question.