Effect of charge fluctuations on the persistent current through a quantum dot

We study coherent charge transfer between an Aharonov-Bohm ring and a side-attached quantum dot. The charge fluctuation between the two substructures is shown to give rise to an algebraic suppression of the persistent current circulating the ring as the size of the ring becomes relatively large. The charge fluctuation at resonance provides a transition between diamagnetic and paramagnetic states. Universal scaling, the crossover behavior of a persistent current from a continuous to a discrete energy limit in the ring, is also discussed.