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UBC Theses and Dissertations

Shubnikov-de Haas measurements and the spin magnetic moment of YBa₂Cu₃O₆.₅₉ Ramshaw, Brad


High-temperature superconductivity (high-Tc) was discovered in 1986 in copper-oxide materials, and since that time the goal of understanding high-Tc has driven the advancement of theoretical and experimental condensed matter physics. Despite the concerted efforts of some of the brightest minds in physics over the past 26 years, there is still no microscopic understanding of these materials. One of the main problems is an uncertainty as to whether Fermi liquid theory, which has been the foundation of our understanding of conventional metals for over 50 years, can be used to describe the strange pseudo-metallic properties of the cuprates. This thesis studies the resistivity of the high-Tc superconductor YBa₂Cu₃O₆+x (YBCO) in magnetic fields up to 70 Tesla. These resistivity measurements show oscillatory behaviour as a function of magnetic field, which is a clear signature of a Fermi surface. The development of an advanced technique (based on a genetic algorithm) for analyzing the oscillatory resistance is presented, and the Fermi surface of YBa₂Cu₃O₆.₅₉ is determined with great precision by analyzing the field, angle, and temperature dependences of the oscillations. Analysis of the data shows that the electronic g factor, related to the strength of quasiparticle spin magnetic moment, does not experience strong renormalization in YBCO, in contrast with previous experimental studies. This lack of renormalization has important implications for theoretical descriptions of YBCO. A full description of the shape of the Fermi surface of YBCO is presented, and measurements of YBCO with different oxygen concentrations give the evolution of the Fermi surface with hole doping. A novel technique for fine-tuning the hole doping in YBCO is presented in the context of a Hall coefficient experiment. The result is a detailed doping dependence of the Hall coefficient, indicating that the Fermi surface seen in quantum oscillation experiments is influenced by some type of electronic order---such as charge and spin stripe order---competing with superconductivity near 1/8th hole doping. The behaviour of the superconducting vortex lattice in a magnetic field is analyzed as a function of temperature, and this behaviour also indicates that something is competing with superconductivity near 1/8th doping.

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