  Realizing hybrids of low-dimensional Kondo lattices and superconducting
substrates leads to fascinating platforms for studying the exciting physics of
strongly correlated electron systems with induced superconducting pairing.
Here, we report a scanning tunneling microscopy and spectroscopy study of a new
type of two-dimensional (2D) La-Ce alloy grown epitaxially on a superconducting
Re(0001) substrate. We observe the characteristic spectroscopic signature of a
hybridization gap evidencing the coherent spin screening in the 2D Kondo
lattice realized by the ultrathin La-Ce alloy film on normal conducting
Re(0001). Upon lowering the temperature below the critical temperature of
rhenium, a superconducting gap is induced with an in-gap Shiba band arising
from the interaction of residual unscreened magnetic moments with the
superconducting substrate. A positive correlation between the Kondo
hybridization gap and the binding energy of the subgap Shiba band maximum is
found. Our results open up a promising route toward the design of artificial
superconducting Kondo and heavy fermion systems.
