UBC Theses and Dissertations
A probe to study the microwave surface resistance of crystals, of the high temperature superconductor YBCO Gheinani, Ahmad Reza Hosseini
A superconducting cavity resonator has been developed for the systematic study of the microwave surface resistance of high purity (twinned and detwinned), zinc and nickel doped YBaiCu3O7-8 single crystals at 22.7 GHz. We have successfully tested the resonator on three pure and two 0.15% zinc doped samples; one of the measurement was on a pure crystal grown using the newly developed barium zirconate crucibles. Measurements in the geometry Hrf//c show a crossover in the low temperature behavior of samples as the purity is varied; in one of the doped samples we see a crossover to a gapless regime with a residual conductivity that is close to o00, the predicted zero temperature limit for a d-wave superconductor in 2-D. Measurements with Hrf parallel to the ab-plane have allowed us to measure the ab-anisotropy of a 0.15% zinc doped crystal, which we find to be qualitatively similar to the ab-anisotropy of the pure system . Finally, the measurements are compared in the two geometries.
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