Master Thesis Defense by Ana-Elena Țuțueanu – Niels Bohr Institute - University of Copenhagen

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Master Thesis Defense by Ana-Elena Țuțueanu

This thesis is composed of two interconnected parts, the growth of high temperaturecuprate superconducting single crystals, La2xSrxCuO4, using the Travelling Solvent Floating zone method, and the investigation of their morphological, electrical and magnetic properties using various techniques, in particular neutron scattering.

The results from three neutron scattering experiments are presented. In the first experiment the transition temperature between the low temperature orthorhombic and the high temperature tetragonal phases was used to determine the exact doping of two LSCO single crystals which proved to be x = 0.050 ± 0.002 and x = 0.048 ± 0.002. During the second experiment, the origin of an unexpected quartet of incommensurate peaks, with anomalous temperature and magnetic field dependence, in an annealed LSCO sample with x = 0.07, was determined to be multiple scattering inside the crystal. Lastly, the low energy spin fluctuations have been studied in a LSCO single crystal with strontium doping x = 0.08.

The measurements show an unexpected suppression of the inelastic signal with applied magnetic field, contrary to all reported results from the literature. A comparison is drawn between this sample and an oxygen doped LCO+O crystal which, surprisingly, showed the same behavior.