Electronic properties of Pu₁₉Os simulating β-Pu: the strongly correlated Pu phase

We established the basic electronic properties of ζ-Pu₁₉Os, which is a close analogue to β-Pu, and its low-temperature variety, η-Pu₁₉Os. Their magnetic susceptibility is 15% higher than for δ-Pu. A specific heat study of ζ-Pu₁₉Os shows a soft lattice similar to δ-Pu, leading to a low Debye temperature Θ _D  =  101 K. The linear electronic coefficient γ related to the quasiparticle density of states at the Fermi level points to a higher value, 55  ±  2 mJ (mol Pu K²)^-1, compared to 40 mJ (mol K²)^-1 for δ-Pu. The results confirm that β-Pu is probably the most strongly correlated Pu phase, as had been indicated by resistivity measurements. The volume and related Pu-Pu spacing is clearly not the primary tuning parameter for Pu metal, as the β-Pu density stands close to the ground-state α-phase and is much higher than that for δ-Pu. The η-Pu₁₉Os phase has a record γ-value of 74  ±  2 mJ (mol Pu K²)^-1. The enhancement is not reproduced by LDA+DMFT calculations in the fcc structure, which suggests that multiple diverse sites can be the key to the understanding of β-Pu.