Tunable Kondo Behavior in a Bilayer Graphene Quantum Channel.

The interaction between itinerant electrons and localized spins is key to a wide range of electronic phenomena. We present conductance measurements of a quantum point contact (QPC) in bilayer graphene (BLG). Beyond the expected quantized conductance plateaus reflecting spin-and-valley degeneracy, we observe an additional plateau resembling the "0.7 anomaly", exhibiting signatures of Kondo physics, with a Kondo temperature ranging from approximately 0.5 up to well above 5 K at zero magnetic field, corresponding to energies between 43 and 430 μeV. Because the QPC is spin-and-valley degenerate within our experimental resolution (110 μeV), according to the prevailing Kondo model, these results are consistent with a transition between 4-fold degenerate SU(4) and 2-fold degenerate spin-valley locked SU(2) interactions. Furthermore, we break the degeneracy of the lowest subband by an out-of-plane magnetic field and show that Kondo signatures remain, demonstrating the versatility of BLG QPCs.