  Scanning transmission x-ray microscopy has been used to image electric
currents in superconducting films at temperatures down to 20 K. The magnetic
stray field of supercurrents in a thin YBaCuO film is mapped into a
soft-magnetic coating of permalloy. The so created local magnetization of the
ferromagnetic film can be detected by dichroic absorption of polarized x-rays.
To enable high-quality measurements in transmission geometry the whole
heterostructure of ferromagnet, superconductor and single-crystalline substrate
has been thinned to an overall thickness of less than 1 micron. With this novel
technique local supercurrents can be analyzed in a wide range of temperatures
and magnetic fields. A magnetic resolution of less than 100nm together with
simultaneously obtained nanostructural data allow the correlation of local
supercurrents with the micro- and nanostructure of the superconducting film.
