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  • Séminaire des doctorants

    • Lundi 30 avril 14:00-15:30 - Bastien Loret - MPQ, Paris-Diderot

      Superconductivity and pseudogap in cuprates : a tumultuous relationship

      Résumé : Although high T c superconductivity has been discovered more than 29 years,Automatic word wrap
      the mechanism of superconductivity is not yet understood and raises fundamentalAutomatic word wrap
      questions [1]. My talk will be focus on the link betwen superconductivity and theAutomatic word wrap
      pseudogap, its origin remains mysterious. I will report our recent progress to grow single crystals of HgBa2Ca2Cu3O8 (Hg-1223) cuprate with a new self-ux growth technique. The crystals thus synthesized are submilimetric, slightly underdoped and show high surface quality for spectroscopic measurements. Magnetometry and X-Ray diffraction have been performed. We show for the first time that with adequate heat treatment, we can largely underdope the Hg-1223 compound and control its doping level [2]. Our raman spectroscopy study of a slightly underdoped single crystal of Hg-1223 allowed us to observe that the superconducting pair-breaking peak is associated with a dip on its higher-energy side, disappearing together at T c . This result reveals a key aspect of the unconventional pairing mechanism : spectral weight lost in the dip is transferred to the pair-breaking peak at lower energies. This conclusion is supported by cellular dynamical mean-field theory on the Hubbard model, which is able to reproduce all the main features of the Raman response and explain the peak-dip behavior in terms of a nontrivial relationship between the superconducting and the pseudogap [3]. We confirmed this result on others compounds revealing his universality. We tracked this structure with doping on Bi2Sr2CaCu2O8 [4]. The pseudogap survives in the overdoped region and then disappears above p 0.225, which corresponds to the normal state disappearance of the pseudogap in coincidence with a Lifshitz transition. This suggests a vertical ending line of the pseudogap in the T-p phase diagram.

      Lieu : salle 208a, aîle sud LPS, bât 510

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