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

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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 ≲0.5 μm, 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.