Vacillating valence: Solid-state physics

Electrons in one particular solid phase of plutonium are complex characters: while bound to atoms, in a quantum-mechanical mixture of two different valence states, they also roam freely throughout the crystal. The attraction of curium The nuclear properties of the late actinides such as plutonium and curium — familiar as substrates and by-products in nuclear reactors — are well understood. The same cannot be said of their solid-state properties, which do not fit standard models. For example, it is not clear why curium is magnetic, but plutonium is not. New electronic structure calculations have been used to identify the electronic mechanisms responsible for this anomalous behaviour. These reveal that plutonium has an unusual ground state that is a quantum superposition of two distinct atomic valences, whereas curium adopts a magnetically ordered single valence state at low temperatures.