Fractional matching effect of vortices in Bi2Sr2CaCu2O8+y with square lattice of antidots

In order to study the influence of artificial pinning centers on vortex behavior in high-T-c superconductors, we have measured vortex-flow resistance in Bi2Sr2CaCu2O8+y single-crystal thin films with a square array of antidots. In addition to the integer matching effect, which is expected at integer multiples of the first matching field H-1, fractional matching effects have been found as fine dip structures at fields Hf (= fH(1)) (f: fractional number). The observed values off are 1/6, 1/4, 1/3, 1/2, 2/3, and 3/4. While a square lattice of vortices (or unoccupied antidots) can fit on the antidot array for the cases of 1/4 and 1/2 (3/4), different vortex configurations are required to explain for the other fractions, viz., a stripe pattern at 1/3. (C) 2009 Elsevier B.V. All rights reserved.