  Unconventional superconductivity and magnetism are intertwined on a
microscopic level in a wide class of materials, including high-$T_c$ cuprates,
iron pnictides, and heavy-fermion compounds. A new approach to this most
fundamental and hotly debated subject focuses on the role of interactions
between superconducting electrons and bosonic fluctuations at the interface
between adjacent layers in heterostructures. A recent state-of-the-art
molecular-beam-epitaxy technique has enabled us to fabricate superlattices
consisting of different heavy-fermion compounds with atomic thickness. These
Kondo superlattices provide a unique opportunity to study the mutual
interaction between unconventional superconductivity and magnetic order through
the atomic interface. Here, we design and fabricate hybrid Kondo superlattices
consisting of alternating layers of superconducting CeCoIn$_5$ with $d$-wave
pairing symmetry and nonmagnetic metal YbCoIn$_5$ or antiferromagnetic heavy
fermion metals, such as CeRhIn$_5$ and CeIn$_3$. In these Kondo superlattices,
superconducting heavy electrons are confined within the two-dimensional
CeCoIn$_5$ block layers and interact with the neighboring nonmagnetic or
magnetic layers through the interface. In CeCoIn$_5$/YbCoIn$_5$ superlattices,
the superconductivity is strongly influenced by the local inversion symmetry
breaking at the interface. In CeCoIn$_5$/CeRhIn$_5$ and CeCoIn$_5$/CeIn$_3$
superlattices, the superconducting and antiferromagnetic states coexist in
spatially separated layers, but their mutual coupling via the interface
significantly modifies the superconducting and magnetic properties. The
fabrication of a wide variety of hybrid superlattices paves a new way to study
the relationship between unconventional superconductivity and magnetism in
strongly correlated materials.
