The intermetallic compound URu2Si2 is among the best-known cases of correlated electron physics, highlighting the difficulty that we still have accurately describing interactions involving electrons originating in f-orbitals. The most glaring manifestation of our lack of understanding is the Hidden Order phase,characterized by a clear phase transition, but an experimentally undetermined order parameter that remains elusive despite 30 years of looking.
In this talk, I will describe how hybridization between uranium f-electrons and itinerant electrons leads to clear temperature-dependent correlations and a very unusual ground state. I will discuss neutron scattering measurements on Fe-substituted samples, in which Hidden Order transitions to antiferromagnetism, and what we can say about how the electronic structure inboth phases. I will also discuss resonant inelastic x-ray scattering measurements aimed at identifying the degrees of freedom available to the uranium f-electrons and how this relates to the collective low-temperature ground state.