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Microwave surface resistance measurements of YBa2Cu3o6+x single crystals and melt textured slabs employing a niobium double split-ring resonator Dosanjh, Pinder S.

Abstract

The microwave surface impedance of YBa2Cu3O6+x was measured using a new niobium split-ring resonator. For the first time it is shown that this resonator geometry allows one to measure both small single crystals and large area slabs employing the same resonator assembly. By careful polishing of the niobium surfaces the niobium split-ring resonator has achieved a resolution of 0.2µΩ at 2.079GHz, about a factor of 5 better than its predessesor. Results are presented on both the a and b axis at 2.079GHz and 2.942GHz for a high quality YBa2Cu3O6.5 OrthoII single crystal as well as results on two YBa2Cu3O6+x top seeded melt textured slabs. The single crystal results show significant frequency dependence over the narrow range studied, an indication that the width of the Drude peak is less than what has been observed in optimally doped YBa2Cu3O6+x. The scattering rates for both the a and b axis are not well described by a single rate; this is suggestive of two processes contributing to the scattering. As well, the scattering rate in the b direction seems to be impurity limited. Measurements on the two melt textured slabs show that changing the Y2Ba1Cu1O5 concentration from 15-3% has little effect on the surface resistance in the superconducting state. At 77K, the surface resistance for the best slab is only a factor of 1.3 higher than that reported for the best Tl2Ba2Ca1Cu2OΔ thin films. [Scientific formulae used in this abstract could not be reproduced.]

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