  The Kondo effect is a cornerstone in the study of strongly correlated
fermions. The coherent exchange coupling of conduction electrons to local
magnetic moments gives rise to a Kondo cloud that screens the impurity spin.
Whereas complete Kondo screening has been explored widely, realizations of the
underscreened scenario - where only some of several Kondo channels participate
in the screening - remain rare. Here we report the observation of fully
screened and underscreened Kondo effects in quantum dots in bilayer graphene.
More generally, we introduce a unique platform for studying Kondo physics. In
contrast to carbon nanotubes, whose curved surfaces give rise to strong
spin-orbit coupling breaking the SU(4) symmetry of the electronic states
relevant for the Kondo effect, we study a nominally flat carbon material with
small spin-orbit coupling. Moreover, the unusual two-electron triplet ground
state in bilayer graphene dots provides a route to exploring the underscreened
spin-1 Kondo effect.
