  Realizing new classes of ground states in strongly correlated electron
systems continues to be at the forefront of condensed matter physics.
Heavy-fermion materials, whose electronic structure is essentially
three-dimensional, are one of the most suitable systems for obtaining novel
electronic states because they demonstrate many fascinating properties.
Recently, a state-of-the-art MBE technique has been developed to reduce the
dimensionality of the heavy electrons by fabricating heavy fermion
superlattices, which can produce new electronic states present in
two-dimensional (2D) heavy fermion system. In superlattices of
antiferromagnetic heavy fermion CeIn3 and conventional metal LaIn3, the
magnetic order is suppressed by reducing the thickness of the CeIn3 layers. The
2D confinement of heavy fermion also leads to the enhancement of the effective
mass and the deviation from the Fermi liquid properties, which are associated
with the dimensional tuning of quantum criticality. In superconducting
superlattices of heavy fermion superconductor CeCoIn5 and nonmagnetic metal
YbCoIn5, superconductivity is realized even at one-unit-cell-thick layer of
CeCoIn5. The thickness reduction of the CeCoIn5 layers drastically changes the
temperature and angular dependencies of the upper critical field. This result
would be attributed to a suppression of the Pauli pair-breaking effect through
the local inversion symmetry breaking (ISB) at the interfaces of CeCoIn5 block
layers. The importance of the ISB in this system has also been supported by
site-selective nuclear magnetic resonance spectroscopy. In addition, recent
experiment of CeCoIn5/YbCoIn5 superlattices have shown that the degree of the
ISB are controllable, which offers the prospect of achieving even more
fascinating superconducting states. These Kondo superlattices, thus, pave the
way for exploring unusual metallic and superconducting states.
