Extraction of the Complex Resistivity and Pinning Parameters from Microwave Surface Impedance Measurements of Coated Conductors

Abstract

The search for continuous improvement of the magnetic properties of coated conductors requires in-depth knowledge of vortex pinning. Microwave measurements of the superconductor complex resistivity are a very effective tool in obtaining complementary information on vortex pinning, in addition to conventional critical current density $J_c$ measurements. The microwave characterization suffers, however, from geometrical effects when the superconducting films are not thick with respect to the penetration depth, as the high-frequency field leaks through the superconductor and also probes the underlying substrate structure. Whilst the resulting electromagnetic problem has largely been addressed in the case of insulating or semiconducting substrates, metal substrates in coated conductors require further consideration. In this paper, we address the issue of obtaining the microwave resistivity of thin superconducting films grown on metal substrates, with particular emphasis on the correct determination of the vortex parameters. We finally illustrate the extraction procedure on a real sample measurements performed on a YBCO film deposited on metal tape.