UC San Diego

Strongly correlated f-electron systems are a rich reservoir for exotic and intriguing physical phenomena; their competition and interplay between localized magnetic moments in partially filled d- or f-electron shells, and conduction electron states lead to complex magnetism, unconventional superconductivity, and other intricate matter of states. The complex phase diagrams of temperature T versus a control parameter δ, such as chemical composition x, applied pressure P, and magnetic field H, have been observed, where they exhibit new and unexpected physics, including "non-Fermi-liquid" (NFL) behavior, "rattling" motion of atoms in a cage structure, local structure distortion, crossover of superconducting order parameters, and the coexistence of superconductivity and magnetism. In order to explore such new phase diagrams, therefore, the work in this dissertation focuses on several chemical substitution studies on f-electron systems: the layered superconductor La1-xYxO0.5F0.5BiS2, and the filled-skutterudite PrPt4Ge12-xSbx and Pr1-xEuxPt4Ge12 systems, whose parent compound PrPt4Ge12 is an unconventional superconductor. Polycrystalline samples were synthesized during the course of the studies and were characterized by means of x-ray diffraction, electrical resistivity, magnetic susceptibility, and specific heat measurements.