Shapiro steps in superconducting films with a periodic pinning potential

Shapiro voltage steps at voltages V-n=nV(o) occur in the voltage-current ch aracteristics of a superconducting film with a periodic pinning potential i n the presence of rf radiation. We report on their experimental observation in a superconducting film with a square lattice of perforated microholes ( antidots) and on numerical simulations showing the Shapiro steps in the vol tage-current characteristics of the de flux transformer. For the square ant idot lattice, the ratio V-o/v of the step height to the applied rf frequenc y depends on the antidot lattice period d, while in the flux transformer ge ometry this ratio can be tuned by the magnetic field. This tuneability of t he resolution makes the flux transformer a good candidate for applications (e.g. broad-band radiation detection).