Magnetic field observation of a single flux quantum by electron-holographic interferometry

Abstract

The magneitc lines of force of a single flux quantum (fluxon) penetrating a superconducting film (Pb) were observed directly and individually by the electron holography technique using the Aharonov-Bohm effect. The phase contours of the electron wave not only confirm the quantized flux value h/2e but also reveal, by phase amplification, internal structure of a single fluxon. With the film thickness \ensuremath{\lesssim}0.5 \ensuremath{\mu}m, each fluxon, after penetrating the film, fans out or makes a ssU shape returning to another point on the film surface. With thicker films, fluxons form a bundle with a flux amounting to several times h/2e.