Observation of periodic vortex pinning induced by Bitter decoration

In this paper we report on a type of vortex pinning, Bitter pinning. In this technique, a vortex lattice in a type II superconductor, ${\mathrm{NbSe}}_2,$ is decorated with magnetic particles which form clumps on the surface of the sample where the vortices exit. Because of the van der Waals forces, these magnetic dots stay well fixed after the sample is returned to room temperature. We present data showing that these patterns can act as pinning sites for vortices in subsequent experiments. This method allows one, in a simple and effective way, to produce periodic, quasiperiodic, or disordered pinning structures for static and dynamic vortex experiments.