What is the valence of a correlated solid? The double life of delta-plutonium

While the nuclear properties of the late actinides (Pu, Am, Cm) are fully understood and widely applied to energy generation, their solid state properties (elastic, magnetic and electronic) do not fit within the standard model of solid state physics and are the subject of active research 1 . Plutonium displays phase transitions with enormous volume differences among its phases and both its Pauli like magnetic susceptibility and resistivity are an order of magnitude larger than those of simple metals 2 . Curium is also highly resistive but its susceptibility is Curie-like at high temperatures and orders antiferromagnetically 3 at low temperatures. The anomalous properties of the late actinides stem from the competition between the itinerancy and localization of its f electrons, which makes the late actinides elemental strongly correlated materials 4 . A central problem field to understand the mechanism by which these materials resolve these conflicting tendencies.