  Magnetic impurities embedded in a metal are screened by the Kondo effect,
signaled by the formation of an extended correlation cloud, the so-called Kondo
or screening cloud. In a superconductor, the Kondo state turns into sub-gap
Yu-Shiba-Rusinov (Shiba) states, and a quantum phase transition occurs between
screened and unscreened phases once the superconducting energy gap $\Delta$
becomes sufficiently large compared to the Kondo temperature, $T_K$. Here we
show that, although the Kondo state does not form in the unscreened phase, the
Kondo cloud does exist in both quantum phases. However, while screening is
complete in the screened phase, it is only partial in the unscreened phase.
Compensation, a quantity introduced to characterize the integrity of the cloud,
is universal, and shown to be related to the magnetic impurities' $g$-factor,
monitored experimentally by bias spectroscopy.

Strongly Correlated Electrons