Confluence of complex surface impedance and depinning current studies of model defects in Nb films near critical temperature

Studying and manipulation of vortex matter is key to understanding fundamental physics of superconducting materials, improving the properties of superconducting devices, and developing new concepts for superconductor applications. Two major approaches to experimentally characterize vortex dynamics are to measure (i) the (de)pinning current density and flux flow resistance in transport measurements or (ii) surface impedance in resonator based measurements as a function of applied field. In this work we combine both approaches to characterize thin Nb films used in superconducting electronic circuits. We measured the vortex pinning constant, viscous drag, and (de)pinning frequency near the critical temperature using a parallel plate resonator (PPR) technique. In addition, we performed transport measurements to study (de)pinning critical current and the (de)pinning force density as a function of temperature and external magnetic field. The combination of PPR and transport experiments provide results for wide temperature range, which is unachievable by each technique individually. We also compare our experimental results with numerical simulations based on the Ginzburg-Landau equations.