Tuning of Hidden Order and Superconductivity in URu 2 Si 2 by Applied Pressure and Re Substitution
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0986-OO02-03
Tuning of Hidden Order and Superconductivity in URu2Si2 by Applied Pressure and Re Substitution Nicholas P. Butch, Jason R. Jeffries, Benjamin T. Yukich, and M. Brian Maple Department of Physics and Institute for Pure and Applied Physical Sciences, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA, 92093-0360
ABSTRACT Single crystals of URu2-xRexSi2 have been grown via the Czochralski technique. Detailed electrical transport studies under pressure on single crystals of URu2Si2 confirm that the zerotemperature critical field is suppressed smoothly towards an extrapolated critical pressure of 15 kbar, which also corresponds to the accepted critical pressure of the hidden order phase. Improving on previous work on polycrystalline samples, studies of single crystals of URu2-xRexSi2 have provided more precise tracking of the suppression of both the hidden order phase at low doping and the ferromagnetic phase at intermediate Re concentrations. INTRODUCTION Since the discovery that below about 17 K the heavy-fermion superconductor (Tc ≈ 1.5 K) URu2Si2 exhibits an ordered phase with an uncertain order parameter [1-3], this hidden order (HO) phase has been the subject of much experimental and theoretical research. At the core of the mystery is a discrepancy between the large size of a jump in the specific heat at the ordering temperature, and the small size of the staggered antiferromagnetic (AFM) moment observed by neutron scattering in the ordered phase [4]. The specific heat anomaly is consistent with the formation of a partial gap over the Fermi surface [2], although many other scenarios have been proposed [5]. The disagreement in magnitude between specific heat and staggered moment has led some researchers to believe that the small observed moment is either coupled to a different primary order parameter, or arises from a competing magnetic phase. An often-useful experimental approach to the identification of ordered phases is the modification of a material via the application of external magnetic field, external pressure, or chemical substitution. The HO phase of URu2Si2 persists to remarkably high magnetic fields of about 37 T [6], but it is much more sensitive to the application of relatively low pressures and chemical substitution onto the Ru site. Early studies of transition metal substitution for Ru in polycrystalline samples found that both the HO/AFM and superconducting phases are suppressed at substituent levels smaller than 10% [7-9]. More recently, it was found that non-Fermi liquid behavior, often associated with a quantum critical point, at which an ordering temperature is driven to 0 K, persists well into the ferromagnetic ordered phase that exists at moderate Re concentration in URu2-xRexSi2, a very unusual occurrence [10]. Early pressure studies on URu2Si2 showed that applied pressure suppresses superconductivity, while the HO/AFM transition temperature is increased [11] and the measured moment grows substantially [12]. However, there still exist disagreements about the r
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