Agenda

Résumé : The origin of high temperature superconductivity (HTS) in cuprates remains highly controversial in spite of an unprecedented research effort for almost 30 years [1]. HTS appears in close proximity to other symmetry-broken states of matter such as antiferromagnetic (AF) insulator and a still mysterious pseudo-gap (PG) phase at moderate doping. In this context, the discovery of hole-doped  Ca₂CuO₂Cl₂  (CCOC) HTS oxychloride cuprates [2-3], such as  Na_xCa_2-xCuO₂Cl₂   (Na-CCOC), is very promising to investigate all these phases on common ground.
In the PG phase, AF excitations (paramagnons) are a promising candidate for being at the basis of this rich phase diagram: opening the pseudo-gap, and perhaps being the boson exchanged in the Cooper pairing, leading to superconductivity.
In this talk, I will show Resonant Inelastic X-ray Scattering measurements, done on doped Na-CCOC, up to the optimally doped region (x=0.18), showing the evolution of the magnon dispersion with doping. We show that the magnon softens along the antiferromagnetic direction ( (110) direction), but persists with the same dispersion along the (100) direction up to the optimal doping.
We also separated the contribution of the magnon from multimagnon dispersion in RIXS spectra using the polarimeter and geometrical methods as used in [4]. We see that the main contribution in the doped samples is due to the magnon while the multimagnon contribution becomes very weak with doping.