Microscopic investigation of enhanced Pauli paramagnetism in metallic Pu$_2$C$_3$

TL;DR

This study combines experimental and theoretical methods to reveal that Pu$_2$C$_3$ exhibits enhanced Pauli paramagnetism with weak electronic correlations and a delocalized 5f-electron band, providing insights into actinide metallic behavior.

Contribution

It presents a comprehensive investigation of Pu$_2$C$_3$'s structural and electronic properties, highlighting the weak correlations and delocalized 5f electrons through combined experimental and computational analysis.

Findings

Enhanced Pauli paramagnetism observed

Moderate electronic correlations indicated by Sommerfeld coefficient and Wilson ratio

Narrow 5f bands confirmed near the Fermi level

Abstract

A combined study of the structural and electronic properties of polycrystalline Pu$_2$C$_3$ is reported based on x-ray diffraction, specific heat, magnetic susceptibility, ${}^{13}$C nuclear magnetic resonance (NMR), and band structure calculations. X-ray diffraction reveals a global noncentrosymmetric cubic lattice, with a nearest-neighbor C--C bond length of $r = 1.38$ \r{A}. ${}^{13}$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 $\gamma = 45$ mJ mol$_{\mathrm{Pu}}^{-1}$ K$^{-2}$, with a Wilson ratio $R_W \approx 1.3$ further indicating moderate correlations. ${}^{13}$C nuclear spin-lattice relaxation rate ($1/T_1$) and Knight shift ($K$) measurements find metallic Korringa behavior (i.e., $T_1TK^2=$ const.) with modest ferromagnetic spin fluctuations at low temperature. Taken together, the data point to a delocalized nature of a narrow 5$f$-electron band with weak electronic correlations. Density functional theory band-structure calculations confirm the appearance of such narrow 5$f$ bands near the Fermi level. Our data provide prime evidence for a plutonium-based metallic system with weak electronic correlations, which sheds new light on the understanding of complex paramagnetism in actinide-based metallic compounds.