Suppression of magnetic-flux noise in YBa2Cu3O7−x by a supercurrent

The magnetic-flux noise generated by a patterned film of YBa{sub 2}Cu{sub 3}O{sub 7{minus}{ital x}} is reversibly suppressed by the application of a supercurrent. The total noise power decreases by an order of magnitude, in quantitative agreement with a model involving thermally activated vortex hopping between pairs of pinning sites of nearly equal pinning energy. The model yields a force constant of 6{times}10{sup {minus}5} N/m for a vortex at a typical pinning site, and a hopping distance which increases with temperature from 13 nm at 4.2 K to 64 nm at 60 K. The number density of vortices is at least 0.02 {mu}m{sup {minus}2}, even in a magnetic field of less than 1 {mu}T.