Microwave measurements of powdered YBa2Cu3O7-δ

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Abstract
Microwave measurements on powdered YBa2Cu3O7- delta diluted with Al2O3 are analysed. Approximate values of the complex conductivity sigma (T)= sigma 1-i sigma 2 inside the superconducting grains are deduced, after allowing for their shapes and sizes. sigma 2(T) has BCS form below Tc, corresponding to a penetration depth lambda (0) of 3.8*10-7 m+or-20%. After correction for extraneous losses, sigma 1(T) also has BCS form below Tc. Both sigma 1 and sigma 2 show strong effects from critical fluctuations close to Tc. At higher temperatures the microwave values of sigma 1 are reconciled with the DC resistivity measured on the original sintered material, they show the fluctuation term predicted in the Ginzburg-Landau theory, giving a coherence length xi 0 of about 10-9 m. The material appears to be a metal of low electron density and small resistance ratio, and there is evidence that the gap parameter Delta (T), the electron density of states and the electromagnetic coherence factors are all much as predicted by BCS.