Complete mapping of magnon dispersion in antiferromagnetic layered cuprates using RIXS

In the last decades, the high-temperature superconductivity phenomenon has been widely debated, and even now the physical mechanisms on which it is based are still unknown. However, its correlation with the magnetic properties of the materials in which it shows up has been experimentally probed multiple times; this suggests that a better understanding of the superconductive compounds magnetic interactions is necessary. To this purpose, the Resonant Inelastic X-ray Scattering (RIXS) technique has proven to be a fundamental method to measure the magnon dispersion relation in superconductive cuprate compounds. In particular, the ERIXS (European RIXS) soft X-ray spectrometer, set inside the ID32 beamline in the European Synchrotron Radiation Facility (ESRF), offers at the present time the best energy resolution possible (less than 55 meV at the Cu L3 edge). This instrument has started operations in 2015 and the very first experiment has consisted in the measurement of the magnon dispersion relation for three different layered cuprates compounds: NdBa2Cu3O6.1, Bi2Sr2CuO6+x and CaCuO2. The data analysis is a critical step for understanding the measured samples main features. This procedure however is not univocal, since the theoretical model of high-Tc superconductivity has not been fully developed yet. In this work, the use of the explicit t-J model has been taken into account, and it has been found to be quite insufficient in describing correctly the systems examined. A model based on effective exchange interactions is therefore proposed, which has been implemented in a fitting algorithm thanks to the SpinW Matlab toolbox (from Paul Scherrer Institute). Finally, a physical meaning to the results of the fitting is suggested, correlated to the contribute provided by the apical oxygens of copper ions to the magnetic behaviour of the inspected compounds.