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Superconductivity and pseudogap in cuprates : a tumultuous relationship

Bastien LORET

Séminaire conjoint Matière Condensée et Matière Quantique

Although high Tc superconductivity has been discovered more than 29 years,
the mechanism of superconductivity is not yet understood and raises fundamental
questions [1]. My talk will be focus on the link betwen superconductivity and the
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.

[1] Keimer et al - Nature 518, 179–186 (2015)
[2] B.Loret et al - Inorganic chemistry 56 (16), 9396-9399 (2017)
[3] B.Loret et al - Physical review letters 116 (19), 197001 (2016)
[4] B.Loret et al - Physical review B 96 (9), 094525 (2017)


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