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UBC Theses and Dissertations

[Mu] SR measurement of the magnetic penetration depth in high-TC superconductors Riseman, Tanya Maria


The effect of the magnetic field inhomogeneity in the mixed state of isotropic and anisotropic type II superconductors on the muon polarization in Muon Spin Rotation (μSR) experiments is explored in this thesis. Calculations of the penetration depth from the second and third moments of the muon precession frequency distribution (completely analogous to the NMR Redfield lineshape) are discussed critically for oriented and un-oriented powder samples. In addition, a method of fitting the frequency distribution directly with models which take into account the variability of the penetration depth and the applied field as well as displacements of the flux tubes from their regular positions in the flux lattice is presented. This method allows the penetration depth to be fitted directly from the frequency distribution. The method is demonstrated with μSR data on an unoriented sample of YBa₂Cu₃O₇, using a model of a highly anisotropic superconductor, and on an oriented sample of YBa₂Cu₃O₇, using the isotropic Abrikosov theory, giving a hard-axis penetration depth in YBa₂Cu₃O₇ of approximately 1000 ± 400 Å.

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