Flattened remnant-field distribution in superconducting bilayer

Highlights: • Flattened remnant magnetic field found after turning-off external field. • The investigated system is a superconducting bilayer film. • This field may be the precursor of the fractional vortex. -- Abstract: The remnant magnetic-field distribution was examined in a "flux quantum decomposer (FQD)" [Physica C 548 (2018) 44-49] composed of an ultrathin superconducting bilayer, for determining the formation mechanism of a fractional vortex. A step-like variation in the magnetic-flux distribution between a location on the bilayer and one outside the specimen was observed, after the external magnetic field was switched off. This step-like variation may be explained in terms of the abnormal Meissner effect, which is theoretically predicted, and emerges when one layer has certain defects [Physica C 551 (2018) 41-47]. According to the theory, the flattened distributed magnetic field can be considered as a precursor of the fractional vortex.