Collective response of YBa2Cu3O7/Ag weak-link junction arrays

The collective response of superconducting thin-film arrays of 300×300 coupled YBa2Cu3O7/Ag weak-link junctions is investigated as a function of external magnetic fields. Our highT c arrays, which were fabricated using electron-beam and photolithography techniques, are based on a substrate-induced defect method. In this method, a square array of thin-film Ag lines produces a two-dimensional lattice of junctions in an overlaying thin-film array of highT c lines. We find that the zero-field resistive transition of the array is governed by a Kosterlitz-Thouless-type transition. Below the super-conducting transition, we observe quantum oscillations in magnetoresistance curves at both integer and half-integer multiples of the flux quantum. These results suggest that long-range phase coherence may be established in large highT c arrays.