Pure plutonium is a strongly correlated metal

I often contrast elemental metals to strongly correlated electron materials such as cuprates, organic charge transfer salts, and heavy fermion compounds. However, this is not strictly correct. Some of the lanthanide and actinide elements are strongly correlated metals. This is most clearly demonstrated in the case of cerium and plutonium which undergo isostructural phase transitions involving large volume increases.

This is particularly nicely illustrated in the figure below, taken from a beautiful 2001 Nature news and views by Bob Albers, An expanding view of plutonium. Electronic structure methods based on Density Functional Theory (DFT) completely fail here.

A nice explanation of the figure was given by Savrasov, Kotliar, and Abrahams, in terms of strong electronic correlations that can be captured by Dynamical Mean-Field Theory (DMFT). In particular the expansion from the alpha to the delta phase is associated with a delocalised-localised transition of the f electrons. The lighter actinides have more delocalised f electrons leading to stronger chemical bonding and smaller volumes per atom in the crystal.

The strong correlations are reflected in other properties of plutonium.
This is highlighted in a nice review Plutonium condensed matter physics by Michael Boring and Jim Smith, which contrasts Pu to lighter elemental metals and heavy fermion compounds.

The figure below shows the temperature dependence of the thermal expansion of Pu and Iron. Note the magnitude of the slope is much greater for Pu.

The resistivity of plutonium is compared to potassium (K) and the heavy fermion compound UBe13. The resistivity for Pu is non-monotonic, saturating at a value comparable to the Mott limit, characteristic of a bad metal.