Microwave Characterization of 122-Pnictides by a Superconducting Niobium Cavity

Abstract

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 S11 component of the complex scattering matrix S is measured. The loaded quality factor QLs and the shift of the resonance position are measured during a temperature sweep, followed by calculating of the unloaded quality factor Q0s and the resonance frequencies fLs and f0s by means of the Kajfez procedure where the subscript "s" denotes the sample. The values of the superconducting penetration depth change δλL and of the surface resistance Rs are calculated approximating the single crystal sample by a flat cylindrical disk of appropriate size, based on a procedure described by Maier and Slater.