Synthesis, X-Ray Absorption, and X-Ray Diffraction Spectroscopy Studies of Uranium Based Heavy Fermion Systems

Heavy fermion systems have attracted a great deal of interest since the discovery of the phenomenon in the 1970s. Over the past 35 years, the research in this field revealed a variety of unprecedented properties that the conventional theoretical framework considered conflicting or impossible. The subset of intermetallic compounds containing rare earth and actinide elements is of special interest, as these materials exhibit a range of exotic properties associated with 4f or 5f electrons. A thorough examination of the reports in the literature indicates a delicate interplay between the competing ground states, giving rise to anomalous properties including non-Fermi liquid behavior, unconventional superconductivity, Kondo effect, mixed valence, and unusual magnetic ordering. Given the sensitivity of the competing interactions to external parameters, pressure becomes a crucial non-thermal tuning factor for investigating the exotic properties of these materials and for mapping the rich P-T phase spaces. Our project focused on the synthesis and characterization of multiple uranium based compounds. The 5f electrons are frequently found in the intermediate range between localized and delocalized states in U-based heavy fermion systems. The investigated samples were fabricated at Los Alamos National Laboratory and were probed with X-ray absorption, X-ray emission, and X- ray diffraction spectroscopic techniques at the Advances Photon Source at Argonne National Laboratory. The performed experiments contribute to the understanding of the underlying mechanisms that occur in strongly correlated systems, since a comprehensive theoretical model is yet to be formulated