Mathieu Le Tacon, MPI Stuttgart

Jeudi 7 Novembre 2013, 14h
Amphi Holweck, Esc C, 1ème etage

Charge density waves and electron-phonon coupling in superconducting cuprates : insights from Inelastic photon scattering

Mathieu Le Tacon
MPI Stuttgart

I will present an overview of recent results obtained in high temperature superconducting cuprates obtained by various x-ray scattering and Raman experiments. In the search for the mechanism of HTSC, intense research has been focused on the evolution of the spin excitation spectrum on doping from the AF insulating to the superconducting state of the cuprates. We used RIXS to show that a large family of superconductors (YBa2Cu3O6+x) exhibits damped spin excitations with dispersions and spectral weights closely similar to those of magnons in undoped cuprates [1,2]. In addition to magnetic excitations, RIXS is also sensitive to charge. The greatly enhanced sensitivity of the scattering signal to the valence electron system led us to the discovery of a fluctuating charge density wave competing with the superconducting order at low doping levels [3-5]. Using high resolution inelastic x-ray scattering, we observe a central peak analogous to those observed in conventional CDW systems and attributed to pining of CDW nano-domains on defects. The study of low energy phonons with wavevectors near the CDW ordering vector, also revealed extremely large superconductivity induced lineshape renormalizations as well as anomalous normal state broadening. This provides important
insights regarding the long-standing debate of the role of the electron-phonon interaction, a major factor influencing the competition between collective instabilities in correlated-electron
materials [6]. Finally I will show how unambiguous signatures of the CDW can be detected using more conventional inelastic scattering of visible light (Raman scattering) [7].

[1] M. Le Tacon et al., Nat. Phys. 7, 725 (2011).
[2] M. Le Tacon et al., Phys. Rev. B. 88, R020501 (2013).
[3] G. Ghiringhelli et al., Science 337, 821 (2012).
[4] A. J. Achkar et al., Phys. Rev. Lett. 109, 167001 (2012).
[5] S. Blanco-Canosa et al., Phys. Rev. Lett. 110, 187001 (2013).
[6] M. Le Tacon et al., to appear in Nat. Phys. (2013).
[7] M. Bakr et al., in preparation (2013).

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