Maximizing superconducting coupling strength in heavy-fermion hybrid superlattices of CeCoIn$_5$/CeRhIn$_5$

Interplay between superconductivity and magnetism continues to provide central topics in condensed matter physics. Among others, Ce{\it T}In$_5$ ({\it T} = Co, Rh) compounds offer one of the suitable platforms for the study of this important issue. An intriguing issue concerns coexistence of superconductivity and antiferromagnetism which could be realized at an artificial interface of different materials, but it is not clear how the two different states are affected each other at the interface. Here, by molecular beam epitaxy, we fabricate hybrid superlattices consisting of alternating layers of superconducting CeCoIn$_5$ and antiferromagnetic CeRhIn$_5$. In the hybrid superlattices, we found the presence of both superconducting and antiferromagnetic phases. At ambient pressure, the superconductivity is strongly Pauli limited. On the other hand, with approaching to the quantum critical point of CeRhIn$_5$ layers under applied pressure, the superconductivity is no longer Pauli limited. These results provide the evidence of maximizing superconducting coupling strength in a superlattice structure built of superconducting layer and quantum critical layer.