Electron holography observation of vortex lattices in a superconductor

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Abstract
Magnetic lines of force penetrating a superconducting Nb thin film have been directly observed by electron holography. The tilted specimen is examined in the ‘‘transmission’’ mode that allows the 2D magnetic flux distribution to be discerned in an interference micrograph. The phase distribution of the electron wave transmitted through the specimen has been quantitatively measured. It was found that a 2D array of tiny regions, where the phase distribution rapidly changed, coincided spatially with the spots observed by Lorentz microscopy, and furthermore, these regions were identified to be quantized vortices each having a flux of h/2e by comparing with theoretical calculations.