Microwave Characterization of 122-Pnictides by a Superconducting Niobium Cavity

We present first results of our microwave measurements of Ba1-xKxFe2As2 (with x = 0:34) single-crystal pnictide, using a cylindrical superconducting niobium microwave cavity, working at approximately 26.2 GHz in the TE011-mode. The measured samples, after initial magneto-optic tests of their uniformity, are cut and glued on a sapphire rod, whose temperature can be independently controlled between 5 K and 40 K. Microwave measurements are performed by a vector network analyzer in the reflection mode, i.e. the S-11 component of the complex scattering matrix S is measured. The loaded quality factor Q(Ls) and the shift of the resonance position are measured during a temperature sweep, followed by calculating of the unloaded quality factor Q(0s) and the resonance frequencies f(Ls) and f(0s) by means of the Kajfez procedure where the subscript s denotes the sample. The values of the superconducting penetration depth change delta lambda(L) and of the surface resistance R-s are calculated approximating the single crystal sample by a flat cylindrical disk of appropriate size, based on a procedure described by Maier and Slater.