Pressure effects in Ce and Yb-based HF compounds

Jaccard, D.; Link, P.; Vargoz, E.; Alami-Yadri, K.

doi:10.1016/s0921-4526(96)00689-8

Cited by 18 publications

(11 citation statements)

References 5 publications

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“…For instance, YbCu 2 Si 2 is an intermediate valence system at P = 0 and its magnetic resistivity shows a single maximum at T max ≈ 150 K, as for CeCu 2 Ge 2 at ∼ 22 GPa. By contrast, the resistivity of YbCu 2 Si 2 at ∼ 22 GPa has regained two maxima [11], as observed for CeCu 2 Ge 2 at P = 0, because k B T K has become much smaller than the crystal field energies. Hence more generally, pressure qualitatively acts as a mirror between Ce and Yb compounds.…”

Section: Ytterbium-based Compoundsmentioning

confidence: 73%

See 1 more Smart Citation

Transport Properties of Heavy Fermion Compounds.

Jaccard

Vargoz

Alami-Yadri

et al. 1998

THE REVIEW OF HIGH PRESSURE SCIENCE AND TECHNOLOGY

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A technique for measuring the electrical resistivity and absolute thermopower is presented for pressures up to 30 GPa, temperatures down to 25 mK and magnetic fields up to 10 T. With the examples of CeCu 2 Ge 2 and CeCu 2 Si 2 we focus on the interplay of normal phase and superconducting properties. With increasing pressure, the behaviour of CeCu 2 Ge 2 evolves from that of an antiferromagnetically ordered Kondo system to that characteristic of an intermediate valence compound as the Kondo temperature increases by about two orders of magnitude. In the pressure window 8-10 < P < 20 GPa, a superconducting phase occurs which competes at low pressure with magnetic ordering. For CeCu 2 Si 2 the effective mass of carriers is probed by both the coefficient of the Fermi liquid law and the initial slope of the upper critical field. The magnetic instability is studied notably for CeRu 2 Ge 2 and Yb-based compounds for which pressure-induced magnetic ordering tends to develop. Finally, contrary to conventional wisdom, we argue that in heavy fermions a large part of the residual resistivity is most likely not independent of temperature; tentatively ascribed to Kondo hole, it can be very pressure as well as sample dependent.[electrical resistivity, thermoelectric power, heavy fermion, magnetic order, superconductivity]

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Section: Ytterbium-based Compoundsmentioning

confidence: 73%

“…For intermediate P, the apparent linear T-behaviour of ρ (up to about 15 K i.e. ∼ 5 T A for P = 16 GPa) [11] is an artefact due to the change of the ρ(T) curvature and to the interplay with the residual term. The results for CeCu 2 Si 2 will improve our understanding of this intriguing link.…”

Section: Cecu 2 Gementioning

confidence: 97%

Transport Properties of Heavy Fermion Compounds.

Jaccard

Vargoz

Alami-Yadri

et al. 1998

THE REVIEW OF HIGH PRESSURE SCIENCE AND TECHNOLOGY

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“…43) The isostructural sister compound CeCu 2 Ge 2 was shown to behave in a very similar way, with a shift of around 10 GPa corresponding to the larger atomic size of Ge. 9,44) Strong evidence for a sharp valence transition in CeCu 2 Ge 2 was presented by Vargoz et al 9,45) They showed that the A coefficient of a Fermi-liquid fit to the resistivity ρ = ρ 0 + AT 2 , when plotted against the lowtemperature maximum in resistivity T max 1 showed the expected relationship A ∝ (T max 1 ) −2 in two regions, with a rapid crossover between them. As T max 1 ∝ T K ∝ γ −1 , where γ is the electronic specific heat coefficient, this corresponds to a crossover from the strongly correlated to weakly correlated branch of the Kadowaki-Woods plot.…”

Section: Cecu 2 Simentioning

confidence: 91%

Valence Instability and Superconductivity in Heavy Fermion Systems

2007

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Many cerium-based heavy fermion (HF) compounds have pressure–temperature phase diagrams in which a superconducting region extends far from a magnetic quantum critical point. In at least two compounds, CeCu 2 Si 2 and CeCu 2 Ge 2 , an enhancement of the superconducting transition temperature was found to coincide with an abrupt valence change, with strong circumstantial evidence for pairing mediated by critical valence, or charge transfer, fluctuations. This pairing mechanism, and the valence instability, is a consequence of a f – c Coulomb repulsion term U fc in the Hamiltonian. While some non-superconducting Ce compounds show a clear first order valence instability, analogous to the Ce α–γ transition, we argue that a weakly first order valence transition may be a general feature of Ce-based HF systems, and both magnetic and critical valence fluctuations may be responsible for the superconductivity in these system

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“…42͒ and CeCu 2 Ge 2 . 43 However, no hint of superconductivity has been observed in U 4 PdGa 12 up to 13.5 GPa and down to 1.3 K.…”

Section: Discussionmentioning

confidence: 99%

Magnetic structure and effects of pressure onU4PdGa12

et al. 2009

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We report on the magnetic structure, thermopower, compressibility, and electrical resistivity under pressure of the recently discovered heavy-fermion antiferromagnet U 4 PdGa 12 . The ordering temperature of the annealed polycrystalline U 4 PdGa 12 is T N ϳ 45.5 K. The magnetic structure has been investigated by neutron diffraction. Extra reflections in the powder spectrum appear below ϳ46 K, in good agreement with macroscopic measurements. The simplest magnetic structure compatible with neutron-diffraction data is a collinear antiferromagnetic structure described by the propagation vector q = ͓001͔. In this case the ordered uranium moment amounts to 1.01͑6͒ B and point along the a axis. Thermopower confirms the heavy-fermion features in this uranium intermetallic with positive and high values of Seebeck coefficient. The magnetic transition is clearly identified and induces an upturn below 45.5 K which is followed by a continuous decrease in S͑T͒ at lower temperature. Electrical resistivity measurements of U 4 PdGa 12 under pressure of up to 13.5 GPa indicate the disappearance of the magnetic ordering temperature T N around P c = 10 GPa while compressibility measurements performed by x-ray diffraction up to 25 GPa do not show any structural phase transition related to this magnetic collapse. At higher pressure ͑p Ͼ 10 GPa͒ and at low temperature, a non-Fermi-liquid behavior is observed, with a T 5/3 dependence of the resistivity. This suggests the possible occurrence of a quantum critical point near P c .

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Pressure effects in Ce and Yb-based HF compounds

Cited by 18 publications

References 5 publications

Transport Properties of Heavy Fermion Compounds.

Transport Properties of Heavy Fermion Compounds.

Valence Instability and Superconductivity in Heavy Fermion Systems

Magnetic structure and effects of pressure onU4PdGa12

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