  The electronic structure of the first Pu based superconductor PuCoGa5 is
explored using photoelectron spectroscopy and a novel theoretical scheme.
Exceptional agreement between calculation and experiment defines a path forward
for understanding electronic structure aspects of Pu based materials. The
photoemission results show two separate regions of 5f electron spectral
intensity, one at the Fermi energy and another centered 1.2 eV below the Fermi
level. The results for PuCoGa5 clearly indicate 5f electron behavior on the
threshold between localized and itinerant. Comparisons to delta phase Pu metal
show a broader framework for understanding the fundamental electronic
properties of the Pu 5f levels in general within two configurations, one
localized and one itinerant.
