Probing the Kondo density of states in a three-terminal quantum ring

By measuring the Kondo effect in a quantum ring connected to three terminals, we show that it is possible to determine which lead is strongly coupled to the ring and gives rise to a Kondo resonance, and which lead is weakly coupled. In the configuration where the ring is strongly coupled to only two leads, we use the third weakly coupled lead to probe the Kondo density of states (DOS). By applying a bias voltage between the two strongly coupled leads, we show directly the splitting of the out-of-equilibrium Kondo DOS.