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Vie et mort du Pseudogap dans l’état normal du cuprate Bi2Sr2CaCu2O8+δ

Abstract : More than thirty years of intensive research, Physics of superconductivity in cooper oxides is still nowadays a big puzzle not resolved. These materials exhibit a complex phase diagrams where different orders coexist. Using electronic Raman scattering, we explored the normal state of Bi2Sr2CaCu2O8+δ, where a mysterious phase sets in, namely the pseudogap. The pseudogap manifests it-self as a partial loss of electronic states density at the Fermi level below a characteristic temperature T∗ which is higher than the critical temperature Tc .So far, it microscopic origin is still unidentified. In the aim to study the pseudogap, we carry out a fine tuned doping study (controlled by oxygen insertion only) in large range of doping level between p=0.08 and p=0.23. Therefore, we succeed to determine the end point of the pseudogap in the normal state at a critical doping pc= 0.22. On other hand, our Raman studies in the normal and superconducting states show an enhancement of the density of states at the Fermi level of the Brillouin zone as the doping level increases. This corresponds to a topological change of the Fermi surface from hole-like to electron-like which occurs at p=0.22. This Fermi surface topological change is known as a Lifshitz transition. Surprisingly, the collapse of the pseudogap coincides with a Lifshitz transition, which is observed in other materials as well. We demonstrate the interplay between the Lifshitz transition and the pseudogap collapse. Further, by exploring the superconducting state, we have found three distinct energy scales, each one corresponds to a specific region of the momentum space. Our measurements show that the doping evolution of the three energy scales is sensitive to the topological change of the Fermi surface and the presence of electronic orders. Finally, we have studied the vibrational modes of Bi2Sr2CaCu2O8+δ and its evolution with doping. We detected a new vibrational modes which are sensitive to the Bi-O plan cleavage, and other are sensitive to the presence of the electronic orders of the phase diagram
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https://hal.archives-ouvertes.fr/tel-01493464
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Submitted on : Tuesday, March 21, 2017 - 4:09:44 PM
Last modification on : Monday, November 9, 2020 - 11:35:08 AM
Long-term archiving on: : Thursday, June 22, 2017 - 2:27:04 PM

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  • HAL Id : tel-01493464, version 1

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Siham Benhabib. Vie et mort du Pseudogap dans l’état normal du cuprate Bi2Sr2CaCu2O8+δ. Electrons fortement corrélés [cond-mat.str-el]. Université Paris 7 - Denis Diderot, 2016. Français. ⟨tel-01493464⟩

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