  Superconductors containing magnetic impurities exhibit intriguing phenomena
derived from the competition between Cooper pairing and Kondo screening. At the
heart of this competition are the Yu-Shiba-Rusinov (Shiba) states which arise
from the pair breaking effects a magnetic impurity has on a superconducting
host. Hybrid superconductor-molecular junctions offer unique access to these
states but the added complexity in fabricating such devices has kept their
exploration to a minimum. Here, we report on the successful integration of a
model spin 1/2 impurity, in the form of a neutral and stable all organic
radical molecule, in proximity-induced superconducting break-junctions. Our
measurements reveal excitations which are characteristic of a spin-induced
Shiba state due to the radical's unpaired spin strongly coupled to a
superconductor. By virtue of a variable molecule-electrode coupling, we access
both the singlet and doublet ground states of the hybrid system which give rise
to the doublet and singlet Shiba excited states, respectively. Our results show
that Shiba states are a robust feature of the interaction between a
paramagnetic impurity and a proximity-induced superconductor where the excited
state is mediated by correlated electron-hole (Andreev) pairs instead of Cooper
pairs.
