  The Josephson effect provides a direct method to probe the strength of the
pairing interaction in superconductors. By measuring the phase fluctuating
Josephson current between a superconducting tip of a scanning tunneling
microscope (STM) and a BCS superconductor with isolated magnetic adatoms on its
surface, we demonstrate that the spatial variation of the pairing order
parameter can be characterized on the atomic scale. This system provides an
example where the local pairing potential suppression is not directly reflected
in the spectra measured via quasipartcile tunneling. Spectroscopy with such
superconducting tips also show signatures of previously unexplored Andreev
processes through individual impurity-bound Shiba states. The atomic resolution
achieved here establishes scanning Josephson spectroscopy as a promising
technique for the study of novel superconducting phases.
