Quantum oscillations in URu2Si2

Bergemann, Christoph; Julian, S. R.; McMullan, G.; Howard, Brandon; Lonzarich, G. G.; Léjay, P.; Brison, J. P.; Flouquet, J.

doi:10.1016/s0921-4526(96)00717-x

Cited by 45 publications

(29 citation statements)

References 8 publications

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“…Thus we obtain 0.017 < ∼ n h < ∼ 0.021 holes/U. The compensation necessarily indicates the presence of electron band, although it is not confirmed by the dHvA experiments [11,12]. The magnitude of the electronic specific heat [2] is five times larger than the estimation taking only the hole band assuming m h = 13m 0 [11].…”

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confidence: 52%

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Exotic Superconducting Properties in the Electron-Hole-Compensated Heavy-Fermion “Semimetal”URu2Si2

et al. 2007

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We show that the charge and thermal transport measurements on ultraclean crystals of URu2Si2 reveal a number of unprecedented superconducting properties. The uniqueness is best highlighted by the peculiar field dependence of thermal conductivity including the first order transition at Hc2 with a reduction of entropy flow. This is a consequence of multi-band superconductivity with compensated electronic structure in the hidden order state of this system. We provide strong evidence for a new type of unconventional superconductivity with two distinct gaps having different nodal topology.The heavy-Fermion compound URu 2 Si 2 has mystified researchers since the superconducting state (T c = 1.5 K) is embedded within the "hidden order" phase (T h = 17.5 K) [1,2,3]. Although several exotic order parameters have been proposed for the hidden order phase [4], it is not identified yet. According to several experimental observations, most of the carriers disappear below T h resulting in a density one order of magnitude smaller than in other heavy-Fermion superconductors [5,6,7]. Superconductivity with such a low density is remarkablesince the superfluid density is very low in some way reminiscent of underdoped cuprates. Moreover, pressure studies reveal that the superconductivity coexists with the hidden order but is suppressed by antiferromagnetic ordering [8].In this Letter, using ultraclean single crystals, we report various anomalous superconducting properties in URu 2 Si 2 . We show that a peculiar electronic structure appearing below the hidden order transition provides an intriguing stage on which a new type of unconventional superconducting state appears.Single crystals of URu 2 Si 2 were grown by the Czochralski pulling method in a tetra-arc furnace. The welldefined superconducting transition was confirmed by the specific heat measurements. The thermal conductivity κ was measured using a standard four-wire steady state method along the a-axis (heat current q a). The contact resistance at low temperatures is less than 10 mΩ.We first discuss the electronic structure below T h . Figure 1 shows the temperature dependence of the resistivity ρ along the a-axis and Hall coefficient R H (solid circles) defined as R H ≡ dρxy dH at H → 0 T for H c in the tetragonal crystal structure. In zero field, ρ depends on T as ρ = ρ 0 + AT 2 below 6 K down to T c . The exceptionally low residual resistivity ρ 0 = 0.48 µΩ cm and large residual resistivity ratio RRR = 670 attest the highest crystal quality currently achievable. R H exhibits an eight-fold increase below T h and attains a T -independent value at low temperatures, associated with a strong reduction of the carrier density. Most remarkably, the magnetoresistance (MR) increases with decreasing temperature and becomes extremely large at the lowest temperatures. The inset of Fig.

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confidence: 52%

“…Such a low carrier density implies Fermi surfaces occupying only a small part of the Brillouin zone. According to de Haas-van Alphen (dHvA) experiments [11,12], one hole band with nearly spherical shape is reported. This band with Fermi momentum k F ≃ 1.8 × 10 9 m −1 contains ∼ 0.017 holes/U.…”

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confidence: 99%

Exotic Superconducting Properties in the Electron-Hole-Compensated Heavy-Fermion “Semimetal”URu2Si2

et al. 2007

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“…We briefly mention that earlier studies of quantum oscillations in URu 2 Si 2 were reported by Bergemann et al, 124 Ohkuni et al, 125 and Keller et al 126 Although the measurements were performed on less well-defined samples, there are some consistencies with the newer data. Bergemann et al report the observation of two orbits, which cross-sectional areas of 1.09 and 0.41 kT for magnetic field along the c axis.…”

Section: Quantum Oscillationsmentioning

confidence: 85%

“…36,92,105,[124][125][126] In earlier experiments, [124][125][126] only a few extremal orbits could be detected. The more recent dHvA and SdH measurements 36,92,105 on purer crystals have provided a consistent set of data for the quantum oscillations in URu 2 Si 2 .…”

Section: Quantum Oscillationsmentioning

confidence: 92%

Electronic structure theory of the hidden-order materialURu2Si2

et al. 2010

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We report a comprehensive electronic structure investigation of the paramagnetic ͑PM͒, the large moment antiferromagnetic ͑LMAF͒, and the hidden order ͑HO͒ phases of URu 2 Si 2 . We have performed relativistic full-potential calculations on the basis of the density-functional theory, employing different exchangecorrelation functionals to treat electron correlations within the open 5f shell of uranium. Specifically, we investigate-through a comparison between calculated and low-temperature experimental properties-whether the 5f electrons are localized or delocalized in URu 2 Si 2 . The local spin-density approximation ͑LSDA͒ and generalized gradient approximation ͑GGA͒ are adopted to explore itinerant 5f behavior, the GGA plus additional strong Coulomb interaction ͑GGA+ U approach͒ is used to approximate moderately localized 5f states, and the 5f-core approximation is applied to probe potential properties of completely localized uranium 5f states. We also performed local-density approximation plus dynamical mean-field theory calculations ͑DMFT͒ to investigate the temperature evolution of the quasiparticle states at 100 K and above, unveiling a progressive opening of a quasiparticle gap at the chemical potential when temperature is reduced. A detailed comparison of calculated properties with known experimental data demonstrates that the LSDA and GGA approaches, in which the uranium 5f electrons are treated as itinerant, provide an excellent explanation of the available low-temperature experimental data of the PM and LMAF phases. We show furthermore that due to a materialspecific Fermi-surface instability a large, but partial, Fermi-surface gapping of up to 750 K occurs upon antiferromagnetic symmetry breaking. The occurrence of the HO phase is explained through dynamical symmetry breaking induced by a mode of long-lived antiferromagnetic spin fluctuations. This dynamical symmetry breaking model explains why the Fermi-surface gapping in the HO phase is similar but smaller than that in the LMAF phase and it also explains why the HO and LMAF phases have the same Fermi surfaces yet different order parameters. A suitable order parameter for the HO is proposed to be the Fermi-surface gap, and the dynamic spin-spin correlation function is further suggested as a secondary order parameter.

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“…20 24) and several heavy fermion compounds. [25][26][27][28][29] The effect is usually thought to arise through the overlap of quasiparticle states outside the vortex core. The amplitude of the oscillations is governed by the magnitude of the field dependent superconducting energy gap.…”

Section: 12mentioning

confidence: 99%

Damping of the de Haas–van Alphen oscillations in the superconducting state ofMgB2

et al. 2004

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The de Haas-van Alphen (dHvA) signal arising from orbits on the π Fermi surface sheet of the twogap superconductor MgB2 has been observed in the vortex state below Hc2. An extra attenuation of the dHvA signal, beyond those effects described in the conventional Lifshitz-Kosevich expression, is seen due to the opening of the superconducting gap. Our data show that the π band gap is still present up to Hc2. The data are compared to current theories of dHvA oscillations in the superconducting state which allow us to extract estimates for the evolution of the π band gap with magnetic field. Contrary to results for other materials, we find that the most recent theories dramatically underestimate the damping in MgB2.

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Quantum oscillations in URu2Si2

Cited by 45 publications

References 8 publications

Exotic Superconducting Properties in the Electron-Hole-Compensated Heavy-Fermion “Semimetal”URu2Si2

Exotic Superconducting Properties in the Electron-Hole-Compensated Heavy-Fermion “Semimetal”URu2Si2

Electronic structure theory of the hidden-order materialURu2Si2

Damping of the de Haas–van Alphen oscillations in the superconducting state ofMgB2

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