| AVS 60th International Symposium and Exhibition | |
| Actinides and Rare Earths Focus Topic | Monday Sessions |
| Session AC+MI+SA+TF-MoM |
| Session: | Actinides and Rare Earths: Experiment and Electron Correlation |
| Presenter: | G. Lander, ITU, Karlsruhe, Germany |
| Correspondent: | Click to Email |
By 1950 the Manhattan Project and the early nuclear industry had a large legacy of new materials that were poorly understood from a physics perspective. The physics of uranium and plutonium are good examples.
By the mid-1960s progress had been made in applying many physical techniques (many of which, such as sensitive transducers to measure elastic constants, had also been a development of WW II) on the actinide elements and many of their compounds, particularly the simple dioxides. Most theoretical treatments considered the elements and their metallic compounds within the framework of d transition-metals, as many properties seemed to follow these metals, rather than those of the 4f lanthanide series.
By the mid-1970s the group at Argonne National Laboratory had shown, inter alia, that a large orbital moment existed in the actinides even if many properties followed itinerant-electron behavior, and the first band-structure calculations showed how difficult it was to resolve this dichotomy.
The discovery of so-called heavy-fermion superconductors, such as UBe13, at Los Alamos National Laboratory in the early 1980s brought considerable prominence to the field and was a precursor, although not recognized at the time, to the discovery of high-Tc materials in 1986. The further discovery (in 2001) of superconductivity at 18 K in PuCoGa5, also at Los Alamos, shows the key importance of the electronic ground state of the 5f electrons and how this drastically affects the physical properties.
Theory has always been “behind” experiments in the actinides; however, the experimental results have proved a sensitive test to the most advanced electronic-structure calculations, such as dynamical mean-field theory (DMFT) within the local-density approximation, so that in some respects the actinides have become a “test bed” for the newest theoretical models.
60 years after some of the pioneering condensed-matter experiments on these materials, we have a far better picture of the actinides, the importance of the orbital moments, the relevance of intermediate coupling, and the criterion that determine whether the 5f states behave as localized or itinerant. However, we do not have predictive theories – they are all reactive. This implies that we still need to maintain an experimental capability, as these materials will be with us a very long time, even if we abandon nuclear energy.
The challenge today is how to maintain and nurture that experimental capability in a climate where even depleted uranium is regarded with suspicion and its handling demands kilograms of paperwork? Without experiments will theory follow?