  Proximity of two different materials leads to an intricate coupling of
quasiparticles so that an unprecedented electronic state is often realized at
the interface. Here, we demonstrate a resonance-type many-body ground state in
graphene, a non-magnetic two-dimensional Dirac semimetal, when grown on SmB6, a
Kondo insulator, via thermal decomposition of fullerene molecules. This ground
state is typically observed in three-dimensional magnetic materials with
correlated electrons. Above the characteristic Kondo temperature of the
substrate, the electron band structure of pristine graphene remains almost
intact. As temperature decreases, however, the Dirac fermions of graphene
become hybridized with the Sm 4f states. Remarkable enhancement of the
hybridization and Kondo resonance is observed with further cooling and
increasing charge carrier density of graphene, evidencing the Kondo screening
of the Sm 4f local magnetic moment by the conduction electrons of graphene at
the interface. These findings manifest the realization of the Kondo effect in
graphene by the proximity of SmB6 that is tuned by temperature and charge
carrier density of graphene.
