Microwave vortex response in the mixed state of HTS YBCO thin films

It´ well known that microwave measurements are very effective for study of dynamic characteristics of vortices in the mixed state of superconductor, such as: viscosity coefficient, Labusch parameter, Hall constant, pinning energy [1]. In contrast to low frequency experiments (e.g., dynamic magnetic susceptibility measurements), microwave measurements in HTS materials provide dynamic studies of vortex matter in the frequency range close to the so-called depinning frequency ω_p. This allows to determine simultaneously such important parameters as viscosity coefficient η and Labusch parameter k_p. In resonant microwave experiments performed on HTS thin films, one obtains magnetic field dependencies of the resonance frequency F₀ and self-quality factor Q₀ of superconducting thin film resonator. These dependencies allow to determine a contribution Δρ(B) to the complex microwave resistivity, which arises due to vortex oscillations in the mixed state of HTS film. The corresponding relation for Δ_ρ(B) looks like: equation (1) Here B - is magnetic induction in the film; d - is the films thickness; Γ - is the resonator geometry factor, determined by a configuration of microwave current flow; Q₀ - is the self-quality factor of superconducting thin film resonator; F₀ - is the resonance frequency.