An apparatus for the measurement of the surface resistance of high temperature superconducting thin films

An apparatus to measure the millimeter-wave surface resistance of thin films of high temperature superconductors has been built. The apparatus consists of a flow cryostat, an open resonator and a swept-frequency millimeter-wave source/detector pair. The flow cryostat is used to cool the experiment to cryogenic temperatures (either 2 K with liquid helium, or 70 K with liquid nitrogen), while keeping a very short distance between the experiment and room temperature. The cryogenic fluid is drawn through the cryostat, and circulates through heat exchangers, absorbing incident heat. The open resonator allows sensitive measurement of the surface resistance of the film at high frequency. The resonator built operates at 117 GHz, and has a Q for copper at 77 K of 39000. The millimeter-wave source and detector are taken from a fixed frequency apparatus, and were modified to provide a frequency sweep capability. The source and detector operate in a band between 116.8 and 117.6 GHz. Measurements were performed on both metallic and superconducting samples. The metallic samples were used as calibration of the geometric factors of the resonator, in order to extract the value of the surface resistance. Four thin films of high temperature superconductors were measured, as a demonstration of the capabilities of the apparatus.Science, Faculty ofPhysics and Astronomy, Department ofGraduat