High field charge order across the phase diagram of YBa₂Cu₃Oy

In hole-doped cuprates there is now compelling evidence that inside the pseudogap phase, charge order breaks translational symmetry. In YBa2Cu3O y charge order emerges in two steps: a 2D order found at zero field and at high temperature inside the pseudogap phase, and a 3D order that is superimposed below the superconducting transition Tc when superconductivity is weakened by a magnetic field. Several issues still need to be addressed such as the effect of disorder, the relationship between those charge orders and their respective impact on the Fermi surface. Here, we report high magnetic field sound velocity measurements of the 3D charge order in underdoped YBa2Cu3O y in a large doping range. We found that the 3D charge order exists over the same doping range as its 2D counterpart, indicating an intimate connection between the two distinct orders. Moreover, our data suggest that 3D charge order has only a limited impact on low-lying electronic states of YBa2Cu3O y

Hidden magnetism at the pseudogap critical point of a high temperature superconductor

The mysterious pseudogap phase of cuprate superconductors ends at a critical hole doping level p* but the nature of the ground state below p* is still debated. Here, we show that the genuine nature of the magnetic ground state in La2-xSrxCuO4 is hidden by competing effects from superconductivity: applying intense magnetic fields to quench superconductivity, we uncover the presence of glassy antiferromagnetic order up to the pseudogap boundary p* ~ 0.19, and not above. There is thus a quantum phase transition at p*, which is likely to underlie highfield observations of a fundamental change in electronic properties across p*. Furthermore, the continuous presence of quasi-static moments from the insulator up to p* suggests that the physics of the doped Mott insulator is relevant through the entire pseudogap regime and might be more fundamentally driving the transition at p* than just spin or charge ordering.Comment: 26 pages, supplementary info include

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

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 endpoint 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 changeis 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 diagramDepuis trente ans de recherches intensives, la physique des oxydes de cuivre supraconducteurs reste une énigme encore non résolue. Ces matériaux présentent des diagrammes de phase complexes où différents ordres de la matière coexistent. Grâce à la diffusion Raman électronique nous avons pu explorer dans l’état normal du composé Bi2Sr2CaCu2O8+δ, une phase étrange nommée pseudogap. Le pseudogap correspond à une perte partielle des états électroniques au niveau de Fermi en dessous d’une température T∗ bien plus élevée que la température critique Tc. Son origine microscopique reste à identifier. Afin d’étudier la phase pseudogap, nous avons mené une étude minutieuse en fonction du dopage en trous (par insertion d’oxygène uniquement) sur une plage de dopage comprise entre p=0.08 et 0.23. Ceci nous a permis de déterminer le dopage critique pc= 0.22 pour lequel le pseudogap disparait. Parallèlement nos mesures Raman dans l’état normal et l’état supraconducteur montrent un renforcement de la densité d’états électroniques au niveau de Fermi de la zone de Brillouin lorsque le dopage augmente. Ceci correspond à un changement topologique de la surface de Fermi appelée la transition de Lifshitz qui apparait également au dopage p=0.22. La coïncidence entre la disparition du pseudogap et la transition de Lifshitz est surprenante et observée également dans d’autres matériaux. Nous expliquons commentla transition de Lifshitz peut tuer le pseudogap. D’autre part en étudiant l’état supraconducteur, nous avons trouvé trois échelles d’énergies caractéristiques qui évoluent de manières distinctes en fonction du dopage. L’évolution de ces trois échelles d’énergie avec le dopage montre qu’elles aussi sont liées au changement topologique de la surface de Fermi et à la présence d’ordres différents. Enfin une étude structurale par diffusion Ra man du composé Bi2Sr2CaCu2O8+δ, nous a permis de suivre l’évolution des modes de vibrations en fonction du dopage. Nous avons identifié de nouveaux modes propres à la manière de cliver les échantillons et découvert que certains modes étaient aussi sensibles aux ordres du diagramme de phase

High field charge order across the phase diagram of YBa2Cu3Oy

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Reduced Hall carrier density in the overdoped strange metal regime of cuprate superconductors

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High field charge order across the phase diagram of YBa2Cu3Oy

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