Climbing the entropy barrier: Driving the single- towards the multichannel Kondo effect by a weak Coulomb blockade of the leads

We study a model proposed recently in which a small quantum dot is coupled symmetrically to several large quantum dots characterized by a charging energy E-c. Even if E-c is much smaller than the Kondo temperature T-K, the long-ranged interactions destabilize the single-channel Kondo effect and induce a flow towards a multichannel Kondo fixed point associated with a rise of the impurity entropy with decreasing temperature. Such an "uphill flow" implies a negative impurity specific heat, in contrast with all systems with local interactions. An exact solution found for a large number of channels allows us to capture this physics and to predict transport properties.