Direct measurement of single-vortex diameters by electron holography

Abstract
The magnetic-field distribution of vortices in single-crystal Nb thin foil specimens has been quantitatively measured with high spatial resolution by electron holography using a 300-kV field-emission transmission electron microscope. The diameters of single vortices were observed to broaden with increasing temperature under constant applied magnetic field. Vortex diameters varied from ∼150 nm at 4.5 K to ∼230 nm at 8 K, in agreement with the expected behavior. While vortices broadened with temperature, the total flux enclosed by them was constant.