  Scattering of superconducting pairs by magnetic impurities on a
superconducting surface leads to pairs of sharp in-gap resonances, known as
Yu-Shiba-Rusinov (YSR) bound states. Similarly to the interference of itinerant
electrons scattered by defects in normal metals, these resonances reveal a
periodic texture around the magnetic impurity. However, the wavelength of these
resonances is often too short to be resolved even by methods capable of atomic
resolution, like scanning tunneling microscopy (STM). Here, we combine a CO
molecule with a superconducting cluster pre-attached to an STM tip to maximize
both spatial and energy resolution. The superior properties of such a
double-functionalized probe are demonstrated by imaging the spatial
distribution of YSR states around magnetic Fe atoms on a Nb(110) surface. Our
approach reveals rich interference patterns of the hybridized YSR state,
previously inaccessible with conventional STM probes. This advancement extends
the capabilities of STM techniques, providing insights into superconducting
phenomena at the atomic scale.
