  Unconventional superconductivity and magnetism are intertwined on a
microscopic level in a wide class of materials. A new approach to this most
fundamental and hotly debated issue focuses on the role of interactions between
superconducting electrons and bosonic fluctuations at the interface between
adjacent layers in heterostructures. Here we fabricate hybrid superlattices
consisting of alternating atomic layers of heavy-fermion superconductor
CeCoIn$_5$ and antiferromagnetic (AFM) metal CeRhIn$_5$, in which the AFM order
can be suppressed by applying pressure. We find that the superconducting and
AFM states coexist in spatially separated layers, but their mutual coupling via
the interface significantly modifies the superconducting properties. An
analysis of upper critical fields reveals that near the critical pressure where
AFM order vanishes, the force binding superconducting electron-pairs acquires
an extremely strong-coupling nature. This demonstrates that superconducting
pairing can be tuned non-trivially by magnetic fluctuations (paramagnons)
injected through the interface, leading to maximization of the pairing
interaction.

Superconductivity;Strongly Correlated Electrons