A BROAD-BAND METHOD FOR THE MEASUREMENT OF THE SURFACE IMPEDANCE OF THIN-FILMS AT MICROWAVE-FREQUENCIES

We present a new technique to measure the complex surface impedance of the mixed state of superconducting thin films over the broad frequenc y range 45 MHz-20 GHz. The surface impedance is extracted from measure ments of the complex reflection coefficient made on the film using a v ector network analyzer. The technique takes advantage of a special geo metry in which the self-fields from currents flowing in the film are e verywhere parallel to the film surface, making it an ideal configurati on in which to study vortex dynamics in superconductors. The broadband nature of the measurement system allows us to explore a region of mag netic field-temperature-frequency parameter space of superconductors p reviously inaccessible with other measurement techniques. The power of the technique is illustrated by measurements on thin films of the hig h temperature superconductor YBa2Cu3O7-delta.