Superconductors in a DC magnetic field: Parameters derived from microwave measurements

The behavior of a superconductor in a DC magnetic field is dictated by the dissipative motion of flux quanta. Pinning of flux quanta improve the current carrying of superconductors, so that an essential part of the design of the devices and systems resides in proper modelling of such physical phenomenon. We present a method to determine the physical parameters affecting flux motion in superconducting materials in a DC magnetic field using nondestructive, high-frequency measurements of the field-induced surface impedance ΔZ(H). We discuss the reliability of the measurements of the flux motion parameters when thermal activation is present. Motivated by the extensive study of high-T_c superconductors with engineered, linearly extended pinning centers, we extend the analysis to include anisotropy and anisotropic properties. Finally, we give examples of the method using measurements of ΔZ(H) on YBa₂Cu₃O_7-x-based materials.