Nanoscale Electrodynamic Response of Nb Superconductors

Our objective is to study the extreme and local electrodynamic properties of Niobium (Nb), and to relate these properties to specific defects that limit the ultimate RF performance of superconducting radio frequency (SRF) cavities made from Nb. Specifically, we wish to develop a microscopic measure of the response of Nb to RF magnetic fields up to the critical field (Hc) at microwave frequencies (few GHz), and at temperatures down to 4.2 K. In order to image the local electromagnetic response in the GHz frequency regime, a magnetic writer from a commercial hard drive is integrated into the near field microwave microscope and operates with the Nb sample in the superconducting state. The microwave response of Nb thin films from a mesoscopic area are found through linear and nonlinear microwave measurements.