Influence of a local magnetic field on the movement of a single vortex pinned in a niobium thin-film direct current superconducting quantum interference device

To avoid pinning of many vortices, we prepared superconducting quantum inte rference devices (SQUIDs) with a square loop of only 1 mu m linewidth. At o ne side of the SQUID, the loop widens to an area of 4 mu mx5 mu m, which of fers enough space for a few vortices. If a vortex is trapped in this pinnin g area, it begins to migrate by thermally activated hopping between the pin ning sites. It was possible to influence the hopping process via a Lorentz force on the vortex produced by a local magnetic field. We were able to sho w that the vortex was located in the extra area of the SQUID loop and not i n any other part of the SQUID. (C) 1999 American Institute of Physics. [S00 03-6951(99)03947-9].