We study the Kondo screening effect generated by a single-electron transistor or quantum dot embedded in a small metallic ring. When the ring circumference $L$ becomes comparable to the fundamental length scale ${\xi }_K^0=ħ{\upsilon }_F/T_K^0$ associated with the bulk Kondo temperature, the Kondo resonance is strongly affected, depending on the total number of electrons (mod4) and magnetic flux threading the ring. The resulting Kondo-assisted persistent currents are also calculated in both Kondo and mixed-valence regimes, and the maximum values are found in the crossover region.

• Received 9 February 2001

DOI:https://doi.org/10.1103/PhysRevLett.86.5558