Narrow commensurate states induced by a periodic array of nanoscale antidots in Nb superconductor

We examine the interactions of the vortex lattice with a periodic square array of holes in a superconducting Nb film. Using high-resolution magnetic-field measurements of electrical losses, extremely narrow states with a magnetic field width reaching 1% of the matching field value are found at the commensurate points. They are accompanied by pronounced harmonic generation in response to ac modulation of the magnetic field or current. We relate these sharp anomalies to a locked commensurate state with characteristics of a Mott insulator. This offers opportunities for applications of superconducting films with periodic hole arrays as sensitive magnetic field detectors. (C) 2003 American Institute of Physics.