IMAGING OF VORTICES IN SUPERCONDUCTORS BY ELECTRON-BEAM SCANNING

Abrikosov vortices trapped in a superconducting tunnel junction and or iented perpendicular to the barrier plane were imaged by electron beam scanning at 1.6 K, We have used NbAlOxNb junctions. As an important f eature, the top Nb electrode was covered with a SiO2 film of 300 nm th ickness, absorbing most of the 5 keV beam energy. The signal generatin g the image is explained by a model, assuming that the beam-induced el ectronic excitations in the SiO2 overlay film are trapped in the local magnetic field protruding from a vortex, resulting in an increased re combination rate. In addition to providing a novel approach to the ima ging of the vortices in superconductors, our results are important for understanding quasiparticle losses in tunnel junction detectors. (C) 1998 American Institute of Physics.