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Center for Nonlinear Studies |
Since its basic physical properties were first reported in the mid 1980’s, URu2Si2 remains one of the most fascinating heavy fermion f-electron materials known. The compound URu2Si2 has an effective mass of ~25 me, where me is the free electron mass, undergoes a second order transition into a so-called “hidden order†(HO) phase at To = 17.5 K, and exhibits unconventional superconductivity that coexists with HO below Tc ≈ 1.5 K. Remarkably, the identity of the order parameter of the HO phase of URu2Si2 has eluded researchers for three decades and constitutes a challenging problem of much current interest. Experiments have revealed that competing interactions in URu2Si2 can be “tuned†by varying the composition (x) of atomic substituents, pressure (P) and magnetic field (H), yielding complex temperature (T) versus x, P and H phase diagrams. These T(x,P,H) phase diagrams contain a rich variety of electronic phases and phenomena, including unconventional superconductivity, antiferromagnetism, ferromagnetism, HO, exotic phases in the vicinity of quantum critical points, and non-Fermi liquid behavior. Recently, our group found that substitution of isoelectronic Fe for Ru suppresses superconductivity and induces a transition from the HO phase to a large moment antiferromagnetic (LMAFM) phase, similar to the behavior of pure URu2Si2 under pressure. Experiments on URu2-xFexSi2 single crystals reveal that the T(x) phase diagram and variation of the U magnetic moment with x in the URu2-xFexSi2 system are consistent with the T(P) phase diagram and evolution of the U magnetic moment with P in URu2Si2. Single crystals of URu2−xFexSi2 provide an opportunity to study the transition from the HO to the LMAFM phase at atmospheric pressure with techniques that cannot be readily performed on URu2Si2 under high pressure (e.g., ARPES, STM, neutron scattering, measurements in high magnetic fields, etc.). Such studies will yield new information about the HO and AFM phases of URu2Si2 and, hopefully, clues to the identity of the order parameter of the elusive HO phase. In this talk, we briefly review the history of research on URu2Si2 and describe some of the emergent phases and phenomena found in experiments in which competing interactions in URu2Si2 are tuned by varying substituent composition, pressure and magnetic field.
Host: Marcelo Jaime