DIRECT MEASUREMENT OF SINGLE-VORTEX DIAMETERS BY ELECTRON HOLOGRAPHY

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