Smearing of charge fluctuations in a grain by spin-flip assisted tunneling

We investigate the charge fluctuations of a grain coupled to a lead via a small quantum dot in the Kondo regime. We show that the strong entanglement of charge and spin flips in this setup results in a stable SU(4) Kondo fixed point, which considerably smears out the Coulomb staircase behavior already in the weak-tunneling limit. This behavior is robust enough to be experimentally observable.