Measurements of Surface Impedance in MgB(2) in DC Magnetic Fields: Insights in Flux-Flow Resistivity

We present the multifrequency measurements of the surface resistance of spark-plasma-sintered MgB [Formula: see text] performed through a dielectric loaded resonator operating at 16.5 and 26.7 GHz. By normally applying magnetic fields ≤1.2 T to the sample surface, we drove it in the mixed state. By means of data-rooted analysis, we found that the sample vortex dynamics could be fully described within a single-component approach. Pinning phenomena were present and characterized by a depinning frequency smaller than the measurement ones. The multiband nature of the superconductor emerged in the flux-flow resistivity, whose field dependence could be interpreted well within theoretical models. By exploiting them, the upper critical field was extracted in the low-temperature range, which exhibited a consistent temperature trend with the values obtained at the onset of the resistive transition near [Formula: see text] , and was well in line with literature data on other polycrystalline samples.