Nanoscale electrodynamic vortex response of Nb superconductors

Our objective is to study the extreme and local electrodynamic properties of 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 to microwave frequency (few GHz) magnetic fields parallel to the surface. Therefore, a magnetic writer from a commercial hard drive is integrated into the microwave microscope. The microscope operates with the Nb sample in the superconducting state. A vortex response of Nb thin films from a mesoscopic area was found by this technique through the temperature dependent third harmonic generation measurement P_3f(T).