Correlated electrons in delta-plutonium within a dynamical mean-field picture

Given the practical importance of metallic plutonium, there is considerable interest(1-3) in understanding its fundamental properties. Plutonium under goes a 25 per cent increase in volume(4) when transformed from its alpha -p hase (which is stable below 400 K) to the delta -phase (stable at around 60 0 K), an effect that is crucial for issues of long-term storage and disposa l. It has long been suspected that this unique property is a consequence of the special location of plutonium in the periodic table, on the border bet ween the light and heavy actinides-here, electron wave-particle duality (or itinerant versus localized behaviour) is important(5). This situation has resisted previous theoretical treatment. Here we report an electronic struc ture method, based on dynamical mean-field theory, that enables interpolati on between the band-like and atomic-like behaviour of the electron. Our app roach enables us to study the phase diagram of plutonium, by providing acce ss to the energetics and one-electron spectra of strongly correlated system s. We explain the origin of the volume expansion between the alpha- and del ta -phases, predict the existence of a strong quasiparticle peak near the F ermi level and give a new viewpoint on the physics of plutonium, in which t he alpha- and delta -phases are on opposite sides of the interaction-driven localization-delocalization transition.