Observation of Kondo Effect in Rhombohedral Graphene Superlattices
Kondo effect in strongly correlated systems arises from the antiferromagnetic coupling between itinerant conduction electrons and localized magnetic moments, giving rise to a variety of exotic quantum phenomena. Two-dimensional moiré superlattice systems provide a highly tunable platform featuring topological flat bands, where Wannier orbitals are spatially confined by the periodic moiré potential and serve as localized magnetic moments, enabling the observable Kondo effect. Here we experimentally demonstrate Kondo interactions in hexalayer rhombohedral graphene moiré superlattices through magneto-transport and temperature-dependent measurements. With increasing magnetic field, the magnetoresistance exhibits an increase-decrease transition across a critical field B_c, while the Hall resistance R_xy undergoes a sign reversal near B_c. Moreover, as temperature decreases, the longitudinal resistance R_xx first increases logarithmically and then decreases following a T^2 behavior, indicating a transition to heavy fermion liquid. These behaviors can be consistently explained by the breakdown of Kondo singlets induced by either magnetic field or temperature, which liberates carriers previously bound to localized moments, thereby enhancing conductivity and altering the dominant carrier type. Furthermore, our results demonstrate that the Kondo interaction can be continuously tuned by both carrier density n and displacement electric field D, and suggest the emergence of a Kondo insulating state. Our findings provide deep insight into the Kondo effect in moiré engineered flat-band systems, paving the path for exploring exotic correlated quantum phases.