  In the quest for exotic superconducting pairing states, the Rashba effect,
which lifts the electron-spin degeneracy as a consequence of strong spin-orbit
interaction (SOI) under broken inversion symmetry, has attracted considerable
interest. Here, to introduce the Rashba effect into two-dimensional (2D)
strongly correlated electron systems, we fabricate non-centrosymmetric
(tricolor) superlattices composed of three kinds of $f$-electron compounds with
atomic thickness; $d$-wave heavy fermion superconductor CeCoIn$_5$ sandwiched
by two different nonmagnetic metals, YbCoIn$_5$ and YbRhIn$_5$. We find that
the Rashba SOI induced global inversion symmetry breaking in these tricolor
Kondo superlattices leads to profound changes in the superconducting properties
of CeCoIn$_5$, which are revealed by unusual temperature and angular
dependences of upper critical fields that are in marked contrast with the bulk
CeCoIn$_5$ single crystals. We demonstrate that the Rashba effect incorporated
into 2D CeCoIn$_5$ block layers is largely tunable by changing the layer
thickness. Moreover, the temperature dependence of in-plane upper critical
field exhibits an anomalous upturn at low temperatures, which is attributed to
a possible emergence of a helical or stripe superconducting phase. Our results
demonstrate that the tricolor Kondo superlattices provide a new playground for
exploring exotic superconducting states in the strongly correlated 2D electron
systems with the Rashba effect.
