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Raman scattering study of underdoped cuprates : effect of doping and external pressure

Mercredi 6 novembre 2013 10:30 - Duree : 1 heure
Lieu : Room 018, Central Building, ESRF - 6 Rue Jules Horowitz - Grenoble

Orateur : Michaela-Sofia SOULIOU (Max Planck Institute for Solid State Research - Stuttgart - Germany)

Understanding the complex phase diagram of cuprates is of pivotal importance for the understanding of high temperature superconductivity. Chemical doping or application of external pressure can be used as tuning parameters between the various phases and to explore the interplay between the competing ground states. Here we present a systematic investigation of the lattice dynamics of the high temperature superconductor YBa2Cu3O6+x by means of Raman spectroscopy, as a function of doping and external pressure. For our study, we have used detwinned single crystals of YBa2Cu3O6+x, with doping levels ranging between x=0.45 (very underdoped) and x=0.95 (optimally doped). Upon cooling, in addition to the Raman modes expected from group theory [1, 2], new Raman active phonons appear for the underdoped samples, at temperatures well above the superconducting transition temperature. The doping and temperature dependence of these new features suggests that they are associated with the recently discovered charge density wave (CDW) [3]. These new modes have been further investigated under high pressure conditions, offering indirect insight in the effect of pressure on the CDW instability. Additional measurements have been performed on the underdoped superconductor YBa2Cu4O8, which thanks to the stoichiometric composition is free of all the complexities introduced by oxygen deficiencies. While no new CDW-induced phonon modes like the ones of underdoped YBa2Cu3O6+x were observed for underdoped YBa2Cu4O8 under ambient or high pressure conditions, our high pressure Raman data reveal the occurrence of a pressure-induced structural phase transition. The lattice dynamics in the new high pressure phase are remarkably different to those of the original phase [4], suggesting drastic changes in the underlying electronic system. References : R. Liu et al., Phys. Rev. B 37, 7971 (1988) M. N. Iliev et al., Phys. Rev. B 77, 174302 (2008) G. Ghiringhelli et al., Science 337, 821 (2012) E. T. Heyen et al., Phys. Rev. B 43, 12958 (1991)

Contact : eva.jahn@esrf.fr

Discipline évènement : (Physique)
Entité organisatrice : (ESRF)
Nature évènement : (Séminaire)
Evènement répétitif : (Séminaire ESRF)
Site de l'évènement : Polygone scientifique

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