Novel electronic phases and competing interactions in the heavy fermion compound URu2Si2

M. Brian Maple (Department of Physics and Center for Advanced Nanoscience, University of California, San Diego)

The heavy fermion compound URu2Si2 undergoes a second order transition at To = 17.5 K into an ordered phase whose identity has eluded researchers for nearly three decades. This so-called hidden order (HO) phase coexists with a type of unconventional superconductivity (SC) that is found below Tc ≈ 1.5 K. The features in the electrical resistivity, specific heat and magnetic susceptibility associated with the HO phase are reminiscent of a charge or spin density wave that forms a gap over about 40% of the Fermi surface below To, with the remainder of the Fermi surface gapped by the SC below Tc. The compound URu2Si2 has been studied extensively by means of a various experimental techniques (e.g., transport, thermal, magnetic, and spectroscopic measurements), and numerous theoretical models have been proposed for the HO phase. In this talk, we describe experimental studies of URu2Si2 under high pressure, high magnetic field, and chemical substitution that have revealed extraordinary behavior and novel electronic phases that are generated by competing interactions. For example, application of pressure suppresses the SC and induces a transition from the HO phase to an antiferromagnetic (AFM) phase at 10 kbar. High magnetic fields suppress the HO phase at ~35 tesla and induce several new electronic phases at higher field, some of which exhibit non-Fermi liquid behavior. Substitution of Re results in the suppression of the SC and the HO transition, the nearby emergence of ferromagnetic (FM) order, and unique critical behavior associated with the FM phase. In contrast, substitution of Fe suppresses SC, induces a transition from the HO phase to an AFM phase, and produces a nearly two-fold increase in temperature of the HO/AFM phase boundary. The support of the US DOE, NNSA, and NSF is gratefully acknowledged.

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