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High-Magnetic-Field Study of the Heavy-Fermion System URu2Si2

Abstract : Heavy-fermion compounds, usually intermetallic compounds of rare-earth elements like Cerium and Ytterbium, or actinides like Uranium, are known for their extraordinary low-temperature physics. Their physics is governed by the hybridization of f- and conduction electrons, which gives rise to the formation of heavy quasiparticles with strongly-enhanced effective masses. URu2Si2 occupies a particular place in the heavy-fermion family. A second-order phase transition at the temperature T0 = 17.5 K is reported by many experimental probes but, despite numerous propositions, no order parameter has been consensually associated to the phase below T0, which is called the "hidden-order" phase. URu2Si2 shows a unique behavior when exposed to strong magnetic fields: a cascade of three first-order transitions between 35 and 39 T drives the system from the paramagnetic hidden-order phase to a high-field polarized paramagnetic state. This work presents a systematic investigation of the magnetic and electronic properties of high-purity URu2Si2 single crystals in intense magnetic fields up to 80 T and at temperatures down to 100 mK. The magnetization and magnetoresistivity experiments presented here have been done in non-destructive pulsed magnetic fields at the Laboratoire National des Champs Magnétiques Intenses of Toulouse (LNCMI-T). The magnetic field-temperature phase diagram of URu2Si2 was studied for the first time in both extended magnetic field H||c (up to 60 T) and temperature (up to 80 K) scales. It indicates that the critical area [35 T-39 T] is initiated by the vanishing of a crossover temperature, which reaches 40-50 K at zero-field. It is demonstrated that this crossover, which probably results from inter-site correlations, is a precursor of the hidden-order phase. An angle-dependent study of the magnetoresistivity, in a wide range of orientations of the magnetic field in the crystal planes (a,a) and (a,c), permitted to establish the angle-dependence of the phase diagram. Magnetization measurements of the Rhodium-doped compound U(Ru0.96Rh0.04)2Si2 revealed a simplified phase diagram, where the hidden-order phase has vanished and where the critical region has been replaced by one intermediate antiferromagnetic phase between 26 and 37 T. The magnetoresistivity is found to be strongly sample-quality dependent and reflects the peculiar electronic properties of URu2Si2. The temperature and field-dependencies of the exceptionally strong magnetoresistivity confirm that the Fermi surface is reconstructed below T0. Crossover-like anomalies in the magnetoresistivity suggest that the Fermi surface is modified in a high-magnetic field H||c far below 35 T, i.e, in the hidden-order phase Quantum oscillations have been observed in the magnetoresistivity for various orientations of the samples in the magnetic field. The Shubnikov-de Haas data confirm that a magnetic field applied along c induces Fermi surface reconstructions inside the hidden-order phase, as indicated by the anomalies observed in the non-oscillating magnetoresistivity. For a magnetic field applied along a, quantum oscillations are observed for the first time up to 80 T and their analysis shows a new frequency branch  with a light effective mass. The angle-dependence of the observed Shubnikov-de Haas frequencies has been established at 1.5 K in high magnetic fields up to 60 T rotating in the (a,a) and (a,c)-planes. This experimental work emphasizes that the f-electron magnetic properties are intimately connected to the properties of the Fermi surface in the hidden-order material URu2Si2.
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Contributor : Gernot Werner Scheerer Connect in order to contact the contributor
Submitted on : Thursday, February 27, 2014 - 11:39:02 AM
Last modification on : Monday, July 4, 2022 - 9:55:46 AM
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  • HAL Id : tel-00952430, version 1


Gernot Werner Scheerer. High-Magnetic-Field Study of the Heavy-Fermion System URu2Si2. Strongly Correlated Electrons [cond-mat.str-el]. Université Paul Sabatier - Toulouse III, 2013. English. ⟨tel-00952430⟩



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