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Open Access Publications from the University of California

Scholarly Works (3 results)

  • Thesis
  • Peer Reviewed
UC San Diego Electronic Theses and Dissertations (2017)

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.

    Cover page: Chemical Substitution Effects on Correlated f-electron Systems
    • Article
    • Peer Reviewed
    UC San Diego Previously Published Works (2017)
    Electrical transport measurements were performed on URu2 - x Fe x Si2 single-crystal specimens in high magnetic fields up to 45 T (DC fields) and 60 T (pulsed fields). We observed a systematic evolution of the critical fields for both the hidden-order (HO) and large-moment antiferromagnetic (LMAFM) phases and established the 3D phase diagram of T-H-x In the HO phase, H/H0 scales with T/T0 and collapses onto a single curve. However, in the LMAFM phase, this single scaling relation is not satisfied. Within a certain range of x values, the HO phase reenters after the LMAFM phase is suppressed by the magnetic field, similar to the behavior observed for URu2Si2 within a certain range of pressures.
      Cover page: Phase diagram of URu2–xFexSi2 in high magnetic fields
      • Article
      • Peer Reviewed
      UC San Diego Previously Published Works (2016)
      Thermal expansion, electrical resistivity, magnetization, and specific heat measurements were performed on URu2-xFexSi2 single crystals for various values of Fe concentration x in both the hidden-order (HO) and large-moment antiferromagnetic (LMAFM) regions of the phase diagram. Our results show that the paramagnetic (PM) to HO and LMAFM phase transitions are manifested differently in the thermal expansion coefficient. The uniaxial pressure derivatives of the HO/LMAFM transition temperature T0 change dramatically when crossing from the HO to the LMAFM phase. The energy gap also changes consistently when crossing the phase boundary. In addition, for Fe concentrations at xc ≈ 0.1, we observe two features in the thermal expansion upon cooling, one that appears to be associated with the transition from the PM to the HO phase and another one at lower temperature that may be due to the transition from the HO to the LMAFM phase.
        Cover page: Phase diagram and thermal expansion measurements on the system URu2−xFexSi2
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