Séminaire LPEM Jacques FLouquet, CEA Grenoble

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12 décembre 2019 14:00 » 15:00 — Amphi Boreau, escalier C 2eme étage

jeudi 12 décembre à 14h00 amphi Boreau, Bat C, 2ème étage

Jacques FLouquet, CEA Grenoble

Supraconductivité des composes d’uranium et ferromagnétisme

Uranium compounds : Ferromagnetism, Fermi Surface and Superconductivity

We will show the progresses realized on the three ferromagnetic (FM) superconductors (SC) UGe2 , URhGe , UCoGe. UGe2 is a key example of the interplay between ferromagnetic (FM) fluctuations and Fermi Surface (FS) reconstruction at each phase transition from ferromagnetic FM2 , FM1 and paramagnetic ones .Special attention is given on the last URhGe and UCoGe cases : transverse magnetic field (H) scan along the b hard axis with respect to the ferromagnetic sublattice magnetization along the c axis induces a collapse of the Curie temperature associated either to H reentrant superconductivity (RSC)in URhGe or to H strong enhancement of the upper critical field(Hc2)in UCoGe . In URhGe , the H tuning of magnetocristalline effect leads to a strong interplay between FM fluctuations along c and b while UCoGe is a clear example of persisting Ising FM fluctuations only along c . In URhGe as well as in UGe2 , the interplay between FM fluctuation and FS reconstruction is strong .These experimental results have pushed to many theoretical proposals. Special attention will be given to Zeeman effect on the band structure. The recent discovery of superconductivity in UTe2 located at the paramagnetic verge of FM instability opens new perspectives .We will show recent works made in high magnetic facilities in LNCMI at Toulouse and Grenoble as well as in ISSP at Tokyo. The spectacular event is that RSC appears sticked to the huge metamagnetic field Hm= 35 T when H is well aligned along the initial hard magnetization axis ; the effects on angular disalignment toward the easy magnetization a axis and the c axis are discussed.

*In collaboration with D Aoki ( Tohoku University) A Miyake ( ISSP-Tokyo) D Braiithwaite , JP Brison, G Knebel, Q Niu ,A Pourret, M Valiska (CEA)C Paulsen ( L Neel) W Knafo, G Seyfarht, I Sheikin (LNCMI)

10 Rue Vauquelin, 75005 Paris