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Mathieu Le Tacon - Max-Planck-Institut für Festkörperforschung, Stuttgart, Germany

Resonant x-ray scattering investigations of high-temperature superconductors

In this talk I will present some recent results obtained from resonant inelastic x-ray
scattering (RIXS) on high temperature cuprates superconductors. We have used RIXS to
study high energy magnetic excitations and found that the YBa2Cu3O6+x family exhibits
damped spin excitations with dispersions and spectral weights similar to those of magnons in
undoped AF cuprates over much of the Brillouin zone. This is in excellent agreement with the
spin excitations obtained by exact diagonalization of the t-J Hamiltonian on finite-sized
clusters. A numerical solution of the Eliashberg equations based on our experimental findings
for YBa2Cu3O7 reproduces its TC within a factor of two, and therefore supports magnetic
Cooper pairing models for the cuprates[1].


In parallel to the observation of magnetic
excitations, we found, in underdoped compounds, a
clear enhancement of elastic scattering around
incommensurate wave vectors (0.31,0,L) and
(0,0.31,L) indicative of the coexistence of charge
ordering and superconducting state. Further
investigation revealed that the charge order survives
in the pseudogap state of these underdoped
compounds, and indicates a competition between the
superconducting instability and long range
incommensurate charge fluctuations[2][3].


[1] Le Tacon, M., et al., Nature Physics, 7, 725-730 (2011).

[2] Ghiringhelli, G., et al., Science, 337, 821-825 (2012).

[3] Achkar, A. J. et al. arXiv:1207.3667 (to appear in PRL)