Mesoscopic kondo screening effect in a single-electron transistor embedded in a metallic ring

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 (0)(K) = h(upsilonF)/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.