Measurements of Surface Impedance in MgB2 in DC Magnetic Fields: Insights in Flux-Flow Resistivity

Abstract

We present the multifrequency measurements of the surface resistance of spark-plasma-sintered MgB2 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 Tc, and was well in line with literature data on other polycrystalline samples.

Concept and preliminary design of dielectric resonator for anisotropic measurement of the surface impedance

“…This feature will prove extremely valuable in the forthcoming design process. Moreover, it has been shown that multifrequency measurements of the surface impedance are of great interest in the study of superconductors [15], [16]. Hence, this becomes an additional design goal, so we choose the TE021 mode as a second operating mode, since it shares (same third index) the same longitudinal configuration and thus induces the same current pattern on the lateral wall.…”