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“High-Tc” Superconductivity in Ce-based Heavy Fermions Compounds - The dominant role of Critical Valence Fluctuations

Mardi 11 septembre 2018 13:30 - Duree : 1 heure
Lieu : LNCMI, salle de conférences "René Pauthenet" (bâtiment J, 2ème étage) - 25 rue des martyrs - 38000 Grenoble

Orateur : Gernot W. SCHEERER (DQMP, University of Geneva, Suisse)

The origin of superconductivity in heavy fermion compounds is a long-standing key issue of condensed matter physics, dating back to the discovery of superconductivity in CeCu2Si2. Most often, superconductivity is considered as being mediated by critical spin fluctuations [1] in the presence of a magnetic instability regime. However, as recently reported in several compounds [2,3,4], optimal superconductivity occurs at the pressure of a valence crossover, which arises from a virtual critical end point at negative temperature Tcr.

For the present study, a method to estimate the temperature Tcr [2] is applied to all top-quality high-pressure electrical resistivity data established in Geneva since 1998, including new data notably from CeAg2Si2, CeRhIn5 and CeIrIn5 (a total of 17 data sets from 9 different compounds). The Ce-based compounds with highest superconducting transition temperature Tc are especially well represented in our work.

The key novelty is that the optimum superconducting Tc of a given sample is mainly controlled by the compound’s Tcr and limited by non-magnetic disorder, which is in line with theory of enhanced valence fluctuations [5]. Moreover, it is found that electrical resistivity most often follows scaling behavior, underlining the dominant role of valence fluctuation physics.

The present study provides compelling evidence for the crucial role of critical valence fluctuations in the formation of Cooper pairs in Ce-based heavy fermion superconductors.

[1] Monthoux, Pines, and Lonzarich, Nature 450, 1177 (2007)

[2] G. Seyfarth et al., Phys. Rev. B 85, 205105 (2012)

[3] Z. Ren et al., Phys Rev. X 4, 031055 (2014)

[4] Ren et al. Phys. Rev. B 96, 184524 (2017)

[5] Onishi and Miyake, J. Phys. Soc. Jpn. 69, 3955 (2000).

Contact : anne-laure.barra@lncmi.cnrs.fr

Discipline évènement : (Physique)
Entité organisatrice : (LNCMI)
Nature évènement : (Séminaire)
Site de l'évènement : Polygone scientifique

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