Fedro, Arthur J.
M.S. (Master of Science)
Department of Physics
Superconductors; Electric conductivity; Fluctuations (Physics); Columnar structure (Metallurgy)--Defects
Introducing columnar defects into high Tc superconductors by heavy ion irradiation is known to be the most effective way to suppress dissipation in the vortex state. It was found tha t even above Tc columnar defects still have a noticeable influence on the conductivity. To account for this effect we calculated the correction to the fluctuation conductivity due to the defects using a time-dependent Ginzburg-Landau approach, with the defects modeled as cylindrical regions with suppressed Tc. For zero magnetic field and for fields far from Hc2) parallel to the columns, we calculated the induced correction with logarithmic accuracy and found tha t it does not depend on the defect strength in the vicinity of Tc. For fields close to Hc2 and parallel to the columnar, defects we obtained the correction exactly within the lowest Landau level approximation (LLL). We analyzed the dependence of the conductivity on the tilting angle of field within a LLL approximation and found that the defect-induced angular dependence is opposite to the anisotropy-induced dependence. We were also able to obtain a logarithmically accurate dependence of the conductivity for large tilting angles. The angular dependencies found can be used to extract quantitative information about parameters of columnar defects.
Milstein, Joshua N., "Fluctuation conductivity in the presence of columnar defects" (1999). Graduate Research Theses & Dissertations. 3158.
ix, 70 pages
Northern Illinois University
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