  Heavy fermion materials have been a rich playground for strongly correlated
physics for decades. However, engineering tunable and synthesizable heavy
fermion materials remains a challenge. We strive to integrate heavy fermion
properties into carbon boron clathrates as a universal structure which can host
a diverse array of interesting physical phenomena. Using a combination of
density functional theory and dynamical mean field theory, we study two rare
earth carbon boron clathrates, SmB$_3$C$_3$ and CeB$_3$C$_3$, and explore
properties arising from the strong electronic correlations. We find a
significant increase in the density of states at the Fermi level in
CeB$_3$C$_3$ as the temperature is lowered, indicating the development of a
heavy electron state. In SmB$_3$C$_3$, a potential Kondo insulating state is
identified. Both findings point to rare earth carbon boron clathrates as novel
strongly correlated materials within a universally tunable structure, offering
a fresh platform to innovate upon conventional heavy-fermion materials design.
