Vortex Motion and Quasiparticle Resistivity in Superconductors at Microwave Frequencies

Abstract

At nonzero frequencies both the normal and super∞uid fractions, as well as moving vortices, contribute to the electrical transport, resulting in intricate expressions for the resistivity. We present an extended study of microwave resistivity data measured on YBa2Cu3O7i‐, SmBa2Cu3O7i‐, and MgB2 by means of a broad-band technique between 2 and 20 GHz and of a resonant system at 50 GHz. We discuss the main experimental flngerprints that allow one to identify the relevance of the difierent contributions from the measured microwave response as a function of frequency, temperature, and magnetic fleld. We show that the fleld-dependent super∞uid/quasiparticles dynamics cannot be in general neglected with respect to the vortex motion, albeit its relative importance is difierent in difierent materials: in high temperature superconductors vortex motion prevails at high flelds, but at low flelds a signiflcant super∞uid/quasiparticle contribution exists (ascribed to the presence of lines of nodes). In MgB2 the two contributions are comparable even at high flelds. In this general frame, we derive from the measurements vortex and super∞uid parameters in agreement with theoretical predictions and independent measurements.