Direct observation of magnetic flux and interstitial vortices in perforated mesoscopic squares of superconducting films

Abstract

We report magnetic visualizations of fluxoid states in perforated mesoscopic squares of superconducting films with a scanning superconducting quantum interference device microscope. The observed magnetic images clearly reveal how the magnetic flux is distributed and trapped in a hole at different magnetic fields. The magnetization determined from the magnetic images exhibits a tilted sawtooth behavior with the magnetic field, indicating the multiple flux quanta trapped in the hole. Further increase of the magnetic field creates an interstitial vortex (vortices) between the hole and the sample edge. The penetration field Hp of the interstitial vortex depends on the sample size and follows a simple relation µ0Hp ≈ Φ0/w2 with the spacing w between the hole and the sample edge.