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La skutterudite PrOs4Sb12: supraconductivité et corrélations

Marie-Aude Méasson 1 
1 LCP - Laboratoire de Cryophysique
SPSMS - UMR 9001 - Service de Physique Statistique, Magnétisme et Supraconductivité : DSM/DRFMC/SPSMS
Abstract : The filled skutterudite PrOs4Sb12 is the first Pr-based heavy fermion superconductor. This thesis addresses several important open questions including the determination of the quasi-particle mass renormalisation, the nature and mechanism of superconductivity, and the intrinsic or extrinsic nature of the double superconducting transition seen in the specific heat.

A fit of the specific heat with magnetic interactions between the ions Pr is proposed. We extract from it an electronic term of between 300-750mJ/K2.mol(Pr). Analysis of the specific heat jump provides evidence that heavy carriers are involved in Cooper pairing and that superconductivity is strongly coupled.
Extensive characterisations by specific heat, resistivity, susceptibility measurements show that a double transition appears in the best samples. Nevertheless we bring the first serious doubts on the intrinsic nature of the double transition, because we have found samples with a single sharp transition at Tc2 and because the ratio of the two specific heat jumps shows strong dispersion among the samples. Furthermore we have measured the superconducting phase diagrams with an A.C. specific heat technique under magnetic field and under pressure up to 4.2 GPa, and we show that the two transitions, Tc1 and Tc2, exhibit similar behaviours with magnetic field and pressure.
We find a strong change in the pressure dependence of Tc's above 2 GPa which might be related to a change in the nature of the superconductivity under pressure (at least partially mediated by fluctuations and only by phonons at respectively low and high pressure) which may be linked to the increase of the crystal field gap of the Pr ions.
Analysis of the upper critical field shows the presence of at least two superconducting bands and concludes to a singlet nature of the pairing.
A strong distortion of the flux-line lattice, which is constant with temperature and field, is obtained by small angle neutron scattering measurement. Further measurement or calculation are needed to distinguish between the explanation based on the presence of nodes in the superconducting gap and the analysis based on the topology of the Fermi surface in a Th symmetry.
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Submitted on : Wednesday, June 7, 2006 - 6:55:08 AM
Last modification on : Friday, March 25, 2022 - 11:10:16 AM
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  • HAL Id : tel-00078647, version 1



Marie-Aude Méasson. La skutterudite PrOs4Sb12: supraconductivité et corrélations. Supraconductivité [cond-mat.supr-con]. Université Joseph-Fourier - Grenoble I, 2005. Français. ⟨NNT : ⟩. ⟨tel-00078647⟩



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